Previously spammed domains (content) - Still usable? (detail

Previously spammed domains (content) - Still usable? (details inside)
I have the following situation.
In an experiment I've registered a batch of expired domains, the kind usually ignored by more experienced folks.
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The backlinks are generally alright, most are clean, tens or hundreds of inbound links. DA ranges from 30 to 40. A bad backlink here and there, can be disavowed with no issues but haven't got to that yet.

The problem with the domains is that they had either japanese content, or sometimes other forms of spammy content for a while. Some were dropped. Some were 301 or 302 redirected. Anyway, one of the things of this kind. Some had no content indexed, but profile looked okay so it was a risk registering them. Multiple owners, multiple types of different content over the years. Most were registered before 2010, some as early as 1999. I must also specify that none of these has a manual action.

The big surprise was, half of these domains are working quite well in Google.

I've thrown 10-20 pages on each for a test. About half of them got pretty nice rankings on certain medium difficulty niches (the sorts where Adwords get $20 a click). Others are indexed too but not so good ranking, still better than any new domain with just a few links. It's not ultra-high performance; but there are enough first page and second page listings on half of it so this can be built further. I know however to avoid using expired domains as money sites. Can put some Adsense on them, but I don't bother with that.

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cointasker.com
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My question to you: Are these expired domains sitll usable as PBNs? Again there seems no indication of them having an issue (despite the tarnished history), got indexed fast, good position in SERPs and keeping it for about 6 months already. No sandbox also (expected). I still wonder though.