Are you asking about the SpecificStationCode variable or something? I think the reason is to load only specific missiles onto the station. This would prevent the plane from loading a missile it was never meant to carry (for example, using the SpecificStationCode=F14 in the Phoenix stations would prevent other AHMs, especially AMRAAMs, from showing up in the Phoenix stations).
The way TMF did it is to have one hardpoint to use two or three sets of different missiles without overlapping. Using the innermost wing pylon as an axample, one weapon station entry (IRM only) would be to carry all R-73s/AA-11s, another weapon station entry using the same hardpoint (IRM, SAHM, AHM) would be used to carry R-27s/AA-10s, and yet another weapon station (AHM only) entry to carry only R-77s/AA-12s. This would prevent other missiles like the R-60 and the like from showing up. For example, this method can be used to prevent the early Su-27 Flankers (and derivatives) from loading R-77s (since they are never wired to fire them).
Also very useful if you need to offset between different types of weapons. However, this method would also resort in lots of weapon station entries, and IIRC there's a limit of 32.