I personally think a lot of schooling fish, will school with other schooling fish if they feel the need… sometimes if they look similar, but that isn’t necessary… talking Cory’s, I have 7 albinos, I believe they are all aeneus, but 2 of them were mature, when we added 5 new babies… the babies have grown now, and the 7 are pretty tight, and school often… I also have 2 black Cory’s that were mature, but separated, they started hanging together once in this tank, and while each are completely tolerant of each other, and are often together, they split at various times…
My South American tetras, I typically buy 6 at a time… 3 different groups of Rummy Noses, all school together, but also the Raccoon, and Pristella’s, which kind of look similar, often school…
And I have a “Noah's arc” ( 2 or 3 of each variety) tank, that are African Tetras with 6 or 7 different varieties, and for the most part, they all school together
I find, that if a fish feels the need to school, it’ll school with most other fish, that have the same need, if there are not enough of their own species to school with…