Apple ID's make assumptions (they strip out the + and everything after it) and it's made it a nightmare to use iTunes Connect. Their multiple account support is still terrible so it's easiest to have an Apple ID per iTunes Connect account. Now I need to setup actual aliases in my GSuite account...
From RFC 2822: "The local-part portion is a domain dependent string."
Headaches await you if your code is making a lot of assumptions about how the originating domain manages that local-part portion.