Fascinating. I’ve farmed a lot of Tubbies (like more than a hundred) but never got an Infinity from them. Yet the sources really do heavily indicate that this is the case for Tubby Bones only which would, if true, explain why I never had one drop.
If true, it would make them a worse source for specific Pearls than their “live” friends, assuming the Infinity has the same mechanics as the others which we can assume is the case until a few double drops (i.e. an Infinity and another Pearl) have been reported. Unfortunately, knowing BL2 it is likely that they really do share a pool which is very unfortunate, especially because the Infinity has been fixed.
However, the Infinity fix happened after the release of TTAoDK which leads me to believe that the Infinity was in Tubby Bones’ pool to begin with to finally give us an alternate source beyond Doc Mercy on Normal mode. So when UVHM2 came along, GBX either forgot or didn’t bothered (my cynicism is speaking here) to remove it from that “special drop” pool (just my title for the sake of this conversation) as the drop data for the Pearls was presumably inserted into a specific pool that fit some criteria (in the case of the original Tubbies that pool was either already existing but simply empty or was created that time), which just so happened to be the same the Infinity was in.
Although a theory, I really don’t see why else this could happen or why they would do that. If my theory holds true, Tubby Bones should rarely be able to drop an Infinity in the other modes and/or UVHM1 as well.
Edit: Actually, looking at that video more closely does confirm my theory at least partially. The Legendary COMs and Pearls don’t drop below 62 (their level, as it is possible to get that stuff if you are, for example, on 61) but the Infinity in that footage is on 60 so the other pool shouldn’t yet drop the Pearls but the Infinity is apparently allowed to, confirming my theory that the Tubby Bones drop it by default. Of course, it could have been a world drop, extreme rarity of that aside, so it isn’t set in stone just yet.