Hmm, great question.
@Lushen do you know?
Anyway,
@veli30, here's the link to 1.12 which is Classic/Vanilla. Some people make a difference and fuss about what it's called. 1.12 is what existed before Blizzard's retail. There are some changes to how the game behaves in some scenarios. Namely sharding, if too many players are in a zone it will ramp up spawn rates. To the best of my knowledge, this is something most cores have started implementing.
Another thing to note: from what I've also seen is that you can connect to classic and vanilla cores with either client. This is what I've seen and could be mistaken. Hopefully,
@Lushen has an answer for us. In the event that
@Lushen doesn't have an answer, I took the liberty of fact-checking myself. I went to CMangos discord and asked for their input and this was the answer I got.
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