Iceshrimp has hacky workarounds for interop reasons with plain JSON consumers who fail to understand the currently canonical fully conformant normal form of "as:Public" and only understand the non-canonical full URI. Hacky workarounds shouldn't be the norm. If one were to build an AS2 validator right now, the validator would produce documents that cause interop issues. That's the problem we're trying to solve. Issues like this prevent validation from being feasible.