Zelda1 drop mechanics.

Very important video game stuff here.

Anatomy of a Zelda 1 kill.
When an enemy is killed, a death sound plays instantly. At the same time, the consecutive counters are increased but not the random counter (bomb and fairy are in fact on separate counters).
At the same time, a death animation begins to run for 21 frames. I call this the death spark.
After 21 frames the spark animation ends, the random counter increments by 1, and a drop is calculated for that enemy based on the counters on that exact frame. Priority is Forced Fairy > Forced Bomb/Rupee > Random.

So, if one enemy is in its death spark, and more are killed, you may get unexpected results.

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Example:

Darkwing entered the raft anteroom with 8 consecutive and random on 9 (meaning next kill was heart, then bomb, then rupee).
He bombed and killed three darknuts.
The first kill was instant on the center darknut. Consecutive goes to 9, random counter doesn't increase yet.

The second and third kills happened shortly after the explosion, as two darknuts on the left and right of the bomb turned into it.
The left one was hit before the death spark from the first kill was completed.  Now the consecutive goes to 10 on a bomb kill.
When the center darknut's spark resolved, the counters were checked and a forced bomb was detected and dropped. This is the moment that the bomb/rupee counter resets. At the same time, the random counter was incremented by 1 to 0 (so the next kill could drop a bomb randomly).
Shortly after the first darknut drops an item, the second darknut's spark resolves and the random counter cycles from 0 to 1. The the second darknut's drop was a lucky random bomb on "1".

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Had the three kills happened simultaneously, the forced bomb overwrites the random chance because they are calculated on the same enemy.
If the second and third darknuts are too late to the bomb party, the first one's death spark resolves with consecutive still on 9.