The fact some of the Flying type Pokemon couldn't be able to learn FLY from the HM until Yellow release (Charizard for instance.)
Since I now play it on a emulator, I can edit the moves using Rhydon.exe (Even if it's cheating, it makes sense for a winged Pokemon.), but hey, at least it's not fully restricted (Able to trade a Flying Charizard from Yellow Version to Red/Blue Version without any problem on the Gameboys.)
And many slight coding errors including the attack moves and if I'm not mistaken, FOCUS ENERGY is actually worse than SPLASH (Ends up lowering the critical rate?)
But any of these mistakes is not enough to break our love to this classic.
Love is based of what you know.