CK3 crashed save game recovery

Step 1
Make a backup copy of your saved game just in case it all goes FUBAR

Step 2
Start game in debug mode so that the IM mode will be cancelled when you save your game.
Load the IM game.

Step 3
This part can be annoying, it's trial and error. You need to play the game up until the day before the date it crashes.

So you'll probably have to play at a faster rate until you narrow the date down to within a couple of days, then rinse/repeat from step 2 up to a couple of days before the crash and then play on slow mode up to the crash in order to narrow down the day before the crash to as close as possible.
Keep an eye on the date as you do this because the game will crash without notice on the day of the corruption.
You should be able to get your pre-crash date to within one or two days of the actual crash date.

Filming this final phase is a good method to get the last pre-crash date on playback.

You want to get the pre-crash date as close to the crash date as possible to minimize loss of events.

Step 4
Once you have arrived at your pre-crash date make a note of it, then save the game which will cancel IM mode for the saved game and exit to lobby.
If you make the mistake of exiting to desktop at any point, you have to remember to restart in debug mode, this is so that you will be able to load the game and exit back out to lobby without actually saving the game, otherwise you may have to start the whole conversion process from IM again.

Also calculate your new post-crash starting date as the pre-crash date plus two days

For this example we'll assume the
    crash date is 22nd September 1066
    pre-crash date is 21st September 1066
    post-crash date is 23rd September 1066


Step 5
Load the newly saved game into a good text editor. Personally I use VSC though Notepad++ is probably equally as good.

5.1 Go to the top of the file and delete the first line which should look something like this
SAV01008c6c616000009919

5.2 search for ironman_manager= which should bring you to a section like this
        can_get_achievements=no
        ironman=yes
    }
    ironman_manager={
        ironman=yes
        date=1066.9.21
        save_game="IM_SANDBOX"
        save_interval=three_months
        storage=local
    }
    date=1066.9.21

5.3 set both ironman variables to "no" without quotes so you end up with this
        can_get_achievements=no
        ironman=no
    }
    ironman_manager={
        ironman=no
        date=1066.9.21
        save_game="IM_SANDBOX"
        save_interval=three_months
        storage=local
    }
    date=1066.9.21

5.4 Note that if the game was an achievement run then the variable can_get_achievements would be set to yes, but due to the debug conversion it will have been toggled to no. You can reset that variable later in step 10.1 so don't despair.

5.5 Notice the date= variables, they should be the pre-crash date you saved the game at
Go to the top of the file
Search for your pre-crash date in the correct format which you can get from that date variable in the ironman_manager block

You are only interested in the first three dates you come across, with the first one being within a few lines of the top of file in a variable called meta_date, and the final two being the one in that ironman_manager block and the one immediately following the ironman_manager block

DO NOT DO A GLOBAL CHANGE

You want to change the pre-crash date to your new starting date only for those three dates, so in our example we would end up with this one near the top of the file
    meta_date=1066.9.23

and this ironman_manager block
    ironman_manager={
        ironman=no
        date=1066.9.23
        save_game="IM_SANDBOX"
        save_interval=three_months
        storage=local
    }
    date=1066.9.23

Step 6
Save the game file at this point to a new name, so if you screw up in the next steps you can always come back  to this point

Step 7
7.1 Go to the top of the file
do a global change of the pre-crash date to the post-crash date

So for our example we would be globally changing 1066.9.21 to 1066.9.23

This will change all running events that would progress on the pre-crash date to now progress on the post crash date, all births set to happen on the pre-crash date to happen on the post-crash date, all deaths that happened on the pre-crash date to have happened on the post-crash-date etc but will not progress anything that was set to progress on the crash date.

7.2 Now go back to the top of the file and globally change a double post-crash date to a single post-crash date, so we would be changing "1066.9.23 1066.9.23" without the quotes to 1066.9.23 because in an advanced game there are very likely to be data that is date sequences and very possible that one or more of those sequences was a pre-crash date followed by post-crash date, so you don't want to end up with a double date sequence, though in truth I have never had any problems when I left them in the save game.

Any events that were set to progress on the crash date will not progress, leaving them in an indeterminate state. I have only eve once run into problems with a few of these events but am experienced enough to have recovered most of them.

7.3 Now you need to change the birth dates for births that would have occurred on crash date so you don't lose them, and this is a manual phase, so search for "unborn={ {" without quotes which will take you to a section like this
        unborn={ {
                mother=62948
                father=19217
                assumed_father=19217
                date=1067.6.8
            }
    {
                mother=62918
                father=19245
                assumed_father=19245
                date=1067.6.8
            }

It is unlikely in an advanced game that the births you're interested in will be at the top of this section, so scroll down looking for your crash date, and for our example you would be looking for date=1066.9.22 so you find a data block like this
    {
                mother=17408
                father=17214
                assumed_father=17214
                date=1066.9.22
            }
    {
change the date to your post-crash date so you end up with
    {
                mother=17408
                father=17214
                assumed_father=17214
                date=1066.9.23
            }
    {
rinse/repeat for all births set to take place on your crash date, the good news is that they will all be in sequence, so if there are 5 births set to take place on your crash date they will all be listed one after the other, you won't have to go looking for more when the next one in the sequence is past your crash date

Step 8
Save your game file as the original save game name

Now if you are paranoid like me, you would make a backup of this file at this point.

Step 9

load the save game into CK3 DO NOT simply press resume in the lobby you must load the edited save game file

Notice the date in the calendar at the bottom right of the screen which should not be your post crash date, for our example this would be 23rd September, 1066
Run the game for a while to see if all is well, I usually crank the speed up at this point as I don't care about the results as long as it does not crash

Step 10
Assuming it all went well you now have a working game starting at post-crash date, so exit the game to desktop this time which is safe as you are still in debug mode so the exit process will not overwrite your edited save game.

You was still in debug mode right?

But if not then you can copy the backed up edited save game file over this save game. You did make a backup of your edited save game file right?

10.1 load this tested edited save game file from Step 8 into your editor
Locate the ironman_manager section and change the ironman variables to yes, so for our example you would end up with this
        can_get_achievements=no
        ironman=yes
    }
    ironman_manager={
        ironman=yes
        date=1066.9.23
        save_game="IM_SANDBOX"
        save_interval=three_months
        storage=local
    }
    date=1066.9.23

If your game was a achievement run don't forget to change the can_get_achievements variable to yes so  you would end up with this
        can_get_achievements=yes
        ironman=yes
    }
    ironman_manager={
        ironman=yes
        date=1066.9.23
        save_game="IM_SANDBOX"
        save_interval=three_months
        storage=local
    }
    date=1066.9.23

But do not change the can_get_achievements variable to yes if you were not doing a achievement run, you cannot use this process to cheese achievements.

10.2 save the game file

Step 11
Restart the game and load the edited game file to continue playing, DO NOT simply resume at the lobby you must load the edited game.



NOTES:
It is possible that your game is crashing two days beyond your identified pre-crash date so for our example pre-crash date of 21st September 1066, the actual crash date could in fact be 23rd September 1066, so if the process did not work try again advancing the post-crash date an extra day.

If your game was an achievement run, don't forget to set the variable can_get_achievements to yes before making your final save.

If your game is crashing instantly when you load, so you cannot find a safe pre-crash date in Step 3 then it should be possible to load the game as in Step 2 then immediately exit to lobby which should still save your game while cancelling IM mode. Then take the file into the editor and look for the meta_date at the top of the file which would be the date the game is trying to start on and can be confirmed in the ironman_manager section. You can calculate your post-crash date from this date but do not perform Step 7.2 for this you will have to do the following
    Step 7.2.1 go to the top of the file and search for "triggered_event={" without the quotes
    Step 7.2.2 search for "played_character={" without the quotes
    Step 7.2.3 cut everything from the point located in 7.2.1 to the point located in Step 7.2.2 and save it in a new file
    Step 7.2.4 now do the original Step 7.2 and Step 7.3
    Step 7.2.5 insert the events you saved in Step 7.2.3 back at the point you located in Step 7.2.1
The problem with this though is that your events that would have been progressed in 7.2 will not be progressed. So it's debatable what effect this will have on your game. An experienced eye could go through the events saved in Step 7.2.3 with a view to saving them but even an experienced eye can be overwhelmed with the sheer number of events in a mature game.

However your game was already screwed before you embarked on this process so roll the dice and go with it, if you save your invested time in a mature game cool, if not then such is life.