From what I understand, the luckiness calculation would be off for many items in the current version, where only some are marked as equalOdds.

Are there decreases based on group sizes still? (Nightbane mount = 100% / groupSize, for example)
How does PL everywhere affect the drop rates? In theory, it shouldn't affect anything unless equalOdd is OFF.

Quote Allara:

Equal Odds is for personal loot, so everything should use it now. Equal Odds OFF causes Rarity to multiply your odds out by the group size, making it much less likely for you to obtain an item. If they changed the drop rate of mounts due to Personal Loot, every single odds in Rarity would have to be re-researched and updated by hand. Good luck with that, haha. Again, Equal Odds should be ON for every item that uses Personal Loot. If that’s the entire game, then just hardcode it to ON in the code that checks it. (Should just be tooltip related code, it’s used for calculating Likelihood/Luckiness.)

This needs to be investigated further.

• Research: Are some drop rates dynamically adjusted by Blizzard? If so, which? Official sources? Tests (NB could easily be done)
• Review DB entries with equalOdds: Does it make sense to have it still? - Should consider current group content only
• Fix: Override all items with equalOdds = ON (Edit: Not doing this for the reasons mentioned below)
• Potentially: Adjust certain item's drop rates based on groupSize if they're being scaled by Blizzard - Only seems to affect the Nightbane mount from Return to Karazhan, which isn't something Rarity would want to track either way

I think 069c97f will be enough, for now. Once BFA is released further adjustments may be necessary, though.

After doing some research, it appears this mostly affects current content (Group Loot).

For Legacy Loot, being in a group COULD change the percentages as loot is apparently divided amongst all party members. However, since this is a fringe case and there isn't any official statement as to how it works with mounts and pets in either scenario, I'm going to ignore the issue for the time being and instead set items obtained from doing current group content to consider group sizes.