MPDCenter

[N. W. Perry]

In the official rules the following is written:
-<Qualifier Number>: Is a sequential number, starting with 1. The qualifier of "-1" is optional and gets added only if there is more than one set that could be assigned the same <Set Number>. The first set using a given number would be understood to never contain the qualifier however numbering should start with the oldest set and some investigation should be done in existing set databases. All subsequent numbers are required.

Example:
6901 - Mobile Lab.mpd (Produced in 1980)
6901-2 - Space Plane.mpd (Produced in 1998)

So I guess the model is the first with that number and the omitted -1 is just added for whatever reason. In my opinion the above is not clear. The current use is: if there is another set with the same name add the -1. When shall we add that? We do not know when the next set with the same name will be released.
Dear LSC, please make this more clear!

There was considerable discussion of that here, for what it's worth.