There is no full 1999 AD map, and trying to piece one together from the 1000 AD and 2300 maps isn't very easy. 1000 and 600 are so similar as to appear that they effectively used the same map. However, they (for some reason) didn't do that with 1999. It seems like it would have been much simpler to have taken the 1000 AD map and changed it for their purposes rather than create a "new" map for 1999AD. Thus, in all likelihood, this map was created fairly on in the development process, possibly when the 1000 AD map didn't exist in its entirety either. There are certainly some familiar landmarks, but the specifics of the map do not match with the specifics of any area in 1000 or 2300.
Though to be fair, 1000 and 600 aren't identical either. Over the course of 400 years new areas appear and old areas vanish (for example, Giant's Claw).
Thus, the 1999 AD map seems to be a bit of an artifact left over from the early stages of development. Since the designers weren't obsessive compulsive like we are, they didn't consider going back to make sure the 1999 ad map matched up with the 1000 or 2300 one.