Isn't the other way around? Vendors already had picked C and they wanted to claim compliance to the then brand new C89 standard so anything they didn't want to

Isn't the other way around? Vendors already had picked C and they wanted to claim compliance to the then brand new C89 standard so anything they didn't want to give up on was deemed "implementation-defined behavior" and anything they couldn't give up on[0] was deemed "undefined behavior". [0] because their machines worked very differently from the others' machines