Any update is going to be backwards incompatible to some extent, even a change to the version number can cause and has caused breakage in software that has bugg

Any update is going to be backwards incompatible to some extent, even a change to the version number can cause and has caused breakage in software that has buggy version checks. Because of that, taking backwards compatibility as an absolute is not useful, and instead we generally limit it to where the old version was being used correctly in supported ways. Whether calling a function with more arguments than it is specified to take is supported will depend on who is maintaining that function, but unless documented I would assume it isn't.