If it is true, I'd guess that it's more so now than back in the old days.
I remember different 12A** models from the same manufacturer being physically different. My Genelec KT88s are larger than the Genelec KT66s of the same vintage that I have. A 7591 was different that 6V6 back then, but now they change the pinout of a 6V6 to make a 7591.....same with 7027 and 6L6 I think.