First of all, is this an old player? Skills can start decreasing for old players, so that would be your culprit there. Otherwise, it depends on what you mean by 'considerably.' If you're talking 20-25%, then something's really weird. If you're talking 5-10%, then you could be right, or the salary calculators could have a systematic error based around a certain configuration of stats and position. Do we even know that the game's salary mechanism used sublevels?
I've been scrounging around the Transfer List. Part of my research is to factor in the fact that a lot of training has been done with some players that are not yet accounted for in salary, so I run the current abilities through the two salary calculators that are available to us. I understand the calculators are estimates, but still . . . I have found one player whose listed salary -- the one he began the season with, and presumably does not reflect any training he may have received this season -- is considerably above that of the estimate given by either salary calculator. What am I to make of this? The player has many skill categories that are just beneath the threshold of being bumped? I don't know what else could explain this. If this is true, then the player is quite a catch, it seems to me.