Theory aside, you'll find that most of the time "fully modded" = "ultimate", in real life, at the particular point in time.
Being "ultimate" replica is only ultimate for a short-to-medium timeframe in rep fora, before a new and better quality part(s) and services are available to rep community members and modders.
Just as an example, an Ultimate 201/A with standard old-school rep case with sappire without A/R, palp crown, V CG, FGD dial, DSN hands etc...is only ultimate until someone comes up with closer to 1:1 part(s) you could update the watch with, like the pre-V case LoS managed to source with screws for double-screws on both lugs etc.
And , as Hooligan said, it's a subjective rating, and it usualy is in the eye of the beholder.
babola