Yes you are right! Christopher Shores and his team of researchers probably missed 131 victories of the mongrel Allied pilots by the experten! And so did the Fighter Group historians who posted the stats here. Possibly due to a Bolshie conspiracy.
It's American sources that differ, there doesn't have to be a conspiracy; the victories of experten or other Axis aces/ pilots have nothing to do with it.
OR - the other possibility is something like "b. "Operational" and "Other" losses include aircraft accidents at base or other friendly territory on a combat mission. Many of these aircraft were not heavily damaged and were flying again after the necessary repairs were made. This condition also exists as regards P-51 aircraft and all loss figures and rates are inflated in this respect. "
Shores et al might be filtering such incidents out especially if they took place at or near the friendly base and not over enemy territory. I don't know.
The losses (casualties) in MAW IV that I counted are to all causes, incl. damaged; in Table 103 of the Digest there are 492 losses to combat & accident for the period mentioned.
I haven't had time to crunch the numbers in MAW IV - I'm rather amazed you apparently have to some extent. Any actual data is always welcome.