We called it the "inverted counter", it seems to be a number that is different for each mesh, but it usually starts from something like 99, 98, 97, etc... however, it doesn't seem to affect anything, even if we leave it zeroed out. The tools use an algorithm that creates this kind of sequence, but really the pattern isn't uniform across models, so the algorithm is just there for the numbers to kind of look like the vanilla ones. In case you decompile a model, the numbers will be stored as inv_count in the ascii, so that the same ones may be used if that model is recompiled.