[lostmyoldone]

According to the tagged union Wikipedia you referenced, a disjoint union is also considered a tagged union. Whether or not that's actually a correct description within the vernacular of computer science, I don't know.

"In computer science, a tagged union, also called a variant, variant record, choice type, discriminated union, disjoint union, sum type or coproduct, ..."

[guerrilla]

They're all what you call isomorphic to eachother, which means roughly any adequate mathematical model of one can mapped to any other.