Yes but those figures/characters have their own place as legitimate characters on screen in the G1 cartoon.
Other recolours have had letters designated to them with their MP number when they re-released moulds as characters from other transformers continuities. Eg: MP11S, MP12G.
Although some might argue that MP13B should have had it's own number given that Soundblaster was a legit character in (Japanese) G1 also. Meh.
You could work on the theory that Mould change = new number with each of those, but then you fall into issues with MP-12G and MP-13B, especially since you get Ratbat there as well....
Then I had a brainwave...
MP-12G, MP-13B, MP-21G, MP-05G are all the SAME CHARACTER as the original, just the Gen 2 version, or electrum coated, or back from the dead.
Also explains why MP-11A and MP-11SW kept Starsceams number, as they had no mould changes (I know, I should open mine and check... might be a different smirk or something) And I think MP-10 EVA is a straight repaint too (might check when i get home from work.... good excuse to get him off the shelf)
And of course if you want an exemption to the rule.... MP-10 A and B had their should leveled of the Autobot insignia, so the Ape/Decepticon tampo could go on.
If they suitably feminize the characters robot mode I may pick it up simply for the novely of having a female Masterpiece figure (is she Bot or Con?). If its just a slightly changed Tracks I wont bother. I got Exhaust for the novelty of the character but other non-TF characters like Tigertracks I've skipped.
Acidstorm is just an imported Hasbro toy, so wasn't going to get a TakaraTomy MP number.... while Skywarp was a Hasbro HK toy, so also wasn't going to get a TakaraTomy MP number (despite them packaging it in a JP box, because they weren't able or willing to use the Hasbro packaging).
So ignore any HK exclusive MP toys that were in Japanese packaging, as TakaraTomy probably wouldn't allow them to use new MP numbers in case they clash with their future numbers.
As for the others that are from TakaraTomy, it seems that the general rule is that after the "reboot" from MP-10, any new character that has remoulding, gets a new number... but new characters that are basically redecos (Tigertrack) and existing characters with new moulding (G2 Sideswipe, Soundblaster) don't get a new number.
(unfortunately, since Ratbat was paired with Soundblaster, it will always remain as an exception to every rule)
Personally I do not care what number it is. With the first lot of MP's being all over the place scale wise I don't think numbering consistency is an issue. I don't have all the Mp's because of scale or because they are characters that mean nothing to me. To me scale is more important than numbering.
Spiderken Away!