Oh yea!!! I've been blowing through mobiles suits left and right with 00 Raiser, Unicorn Gundam and a couple more just to test out.
Well what I find out, is that those 999 values you see is just the "Base Model" (like a car).
Even when you develop a new suit for the same Gundam those 999 values will carry over and add to the new suit
so lets say you pic up Nu Gundam and base values are all 999 well it might have a +14 here, a plus +20 there. It will actually go past 1000. However I noticed regardless if you are 999 or 9999, once you hit 999 that seems to be the strongest and won't make any difference if you go any higher then that. So I think its safe to say that even though the Gundam Max isn't 999 and it's ALOT higher, the cap is 999...after that won't make a difference from 999 to 9999+.
Needless to say, in regards to individual mobile suits and character attributes, I'll make the cap 999 to be safe since it won't make a difference if you exceed it.