I think a dev once explained that a 50% loot chance would be handled correctly in that an internal dice roll would decide if an item drops or not.
Strictly speaking about the
chance of an item being selected as loot, I think that is correct. My own testing has shown the loot probabilities work as expected. What I think is happening with the Loot Abundance setting, specifically, is that it applies after all of the "chance" calculations are done, and it only applies to the quantity of items dropped. In other words, it's not a probability/dice roll thing, it's strictly "multiply the final results by X% and round".
I will do some testing to see if an exact 50% loot abundance allows qty=1 items to drop. I'll try 49% too, to confirm the rounding behavior.
--- an hour later ---
Well, I'm not sure how I'm going to set up the test, because the "count" attribute of a loot item doesn't seem to be working the way I'd expect. I modified the Bookcase loot conatiner like this:
<!-- bookcase -->
<lootcontainer id="49" count="1" size="6,2">
<item name="resourcePaper" count="1" prob="1" />
</lootcontainer>
This was just a test case so I could confirm basic behavior. The expected behavior is to find exactly 1 piece of paper in each bookshelf. Instead I found about 5-8 pieces of paper in each bookshelf. It was always only paper (never books), so I know the mod did correctly restrict the results to only paper, but for some reason the "count" attribute is not working the way the XML documentation says it should. I even tried just removing "count" altogether:
<!-- bookcase -->
<lootcontainer id="49" size="6,2">
<item name="resourcePaper" prob="1" />
</lootcontainer>
Still getting 5-8 paper in every bookshelf. I can't really test Loot Abundance if I can't reliably limit a loot container to give exactly 1 item every time. I think this might even count as a bug, but first I'm going to go dig into resourcePaper a bit. Maybe there's something special about it.
--- 30 minutes later ---
Well there were a couple of other bookshelf-related loot settings (apparently for top half/bottom half bookshelves) and I changed all of them to use the above loot container. Still getting 5-8 paper every time. <shrug> Giving up now.