Yea, there are a couple things that are kind of misleading when it comes to unlocking appearances.
Loot appropriate for Mage, or equipable by Mage ?
Legacy loot is the system that is now in effect for all pre-BfA dungeons and raids, assuming you’re level 120.
When people say that Legacy loot gives you access to stuff from other classes, that’s true, but not universally true.
Example where it works:
Warlocks and Priests and Mages can all equip staves. But not every staff is ment for all 3 classes.
During many prior expansions, we had a stat called “Spirit”, which was often only useful for healers. So a staff with spirit on it, might have originally only dropped for holy/disc priests, and not for mages/warlocks.
As such, they couldn’t unlock that appearance, but now because of legacy loot, anything can drop (even crossbows that none of them can use), and thus all 3 of those classes can get that staff appearance, because they can all equip staves.
Example where it does not:
During many prior expansions, we also had a thing called Tier sets.
These were specific sets (matching legs, chest, helm, …) that belonged to one class only. So Mage’s got one set, Warlocks got another set.
These items have a clear “Classes: Mage” indicator on the tooltip.
As far as i know, you (still) cannot unlock the mage set while on a warlock. While the items can drop, you cannot learn them. Similar to how you can get Plate gear to drop on a warlock, without being able to learn it.
The 2-hour long trading window
The other thing revolves around trading, which isn’t really something you give much thought when you solo an instance, but it still applies.
When you kill a raid- or dungeon boss, the BoP (“binds when picked up”) loot that drops, is immediately soulbound. That prevents you from selling it on the AH or trading it to some random person out in the world. However, the item can for a limited time (2 hours) still be traded between anyone in your party, who was present for the boss kill. If you solo’d the boss, then there’s obviously no one else who meets that criteria, but that doesn’t change anything.
During that 2 hour window, the item will have a blue line of text on the tooltip, to indicate that trading is possible. If you log your character off, that timer pauses (so it’s 2 hours of in-game time). If you equip the item, destroy the item,vendor it, or wait out the 2 hours, then that permanently locks the item to you, and the “can still be traded” thingy no longer applies.
If however, you don’t do any of these things, and just keep the item around in your bags or bank, then the appearance isn’t really fully unlocked yet. Even though once you looted the item you saw a message like:
You have learned appearance X
that was a bit misleading.
Once you vendor/destroy/equip the item, you’ll see the same message again. This time it’s really true.
If you were to trade the item away to someone else after looting it, then you’d (correctly) get a message like:
You have unlearned appearance X
So, generally speaking, after you finish a transmog run you want to vendor all the stuff you looted.