Hello all, I have just joined Team FC and received my WorldTimer last week. In my research and from speaking to other WIS, it seems there are definitely a few variations of this piece. All of which look very similar (different strap colours, minor dial variations, etc) but not all are Limited Editions. I wish this wasnt the case as it makes the actual LE versions less "rare" (at first glance) but in general, I feel LE's are more of a marketing gimmick anyway.
So on to what I've discovered. Now take this with a grain of salt as none of this has been verified by FC.
My understanding is that only the versions with Moscow on the dial are part of the Limited Edition run. This is regardless of strap colour or style. There is a version, much to my amusement, with Canadian cities in place of the US cities on the LE. Being from Toronto, I would have totally bought this version but sadly, i only found out about it after i purchased my US cities version.
Canadian timezones in red to match the maple leaf
Regarding the model number on the case, it definitely wont be too specific as FC uses the same case on several models. But the LE versions will have the number engraved just after the 1888 pieces on the caseback. Here is mine, #1738:
Hope this helps!