"or later" is a hack to get around the fact that the GPL is basically incompatible (I need a better word because this is overloaded) with itself if you change t

"or later" is a hack to get around the fact that the GPL is basically incompatible (I need a better word because this is overloaded) with itself if you change the name. If you want to use GPL and GPLRenamed libraries in the same project the only option is to relicence the project under both licences. This may be possible if you have few dependencies and few authors. But if you want to depend on a new library after some authors have become uncontactable you basically can't.