not sure if you're aware, if this is a intended thing, or a limitation of factorio, but alien drops on surface don't end up in chest from a loaded save (only drops from aliens that die while the chest is placed seem to be going in)

The script only fires when an entity dies and checks for loot, that's intended behavior.

can confirm. i relodaed / ran a few other tests and checked entity-drop locations from earlier in the save and it picked them up once another alien died. i thought it would also fire / trigger the scan for alien loots when the chest was placed. my bad.