The Mustang is a particularly out of the ordinary aircraft to try to "evaluate" by enemy claims compared to total production.
According to one source 15,567 Mustangs (not including A-36s) were built by the end of 1945. And that is a big part of the problem. 6103 of them were built in 1945 and most of those did not see service against Germany. Since just about all, if not all, Mustangs were delivered by ship the Inglewood Mustangs had two choices. 1, Load the preserved for shipment aircraft aboard ships in southern California ports and send them through the Panama canal to an east coast port where the ship will marshaled into a convoy for the voyage across the Atlantic. 2, preserve aircraft and it's engine and take off the wing and crate the wing and fuselage for rail shipment to the east coast or gulf coast to be placed on a ship. The Dallas Mustangs can be placed aboard ship in Texas ports.
In any case it is very unlikely that any Mustang built after Feb 1945 showed up in time to fly against Germany.
Then you have the fact that while the numbers were not huge, Mustangs were being used in the China, Burma, India theater Starting around Sept 1943 with Allison powered versions. First P-51Bs show up in this Theater April 1944.
Going back to the production numbers, 6982 Mustangs were built in 1944 with production increasing from 370 per month in Jan to 720 in Dec.
Going back to 1943 a bit under 3000 Mustangs had been built by Dec 1943 since start of production and that includes the 500 A-36 aircraft.
Granted Spitfires were used around the world too and production continued post war but trying to draw any conclusions based off of claims vs numbers built seems to have a lot of potential problem areas.
Comparing even the B-24 to the B-17 gets difficult because the B-17 was primarily a European bomber with the B-24 seeing much more use in the Pacific, the CBI, for anti-sub patrols and cargo use. Actual numbers used against Germany might be much closer if not favoring the B-17 rather than in proportion to the numbers built.
The claims list is a very good piece of work and a valuable tool but it doesn't seem it can be used on it's own to draw conclusions unless the use of the compared planes is fairly close to begin with, like Lancaster vs Halifax. Somebody will probably point out that I am wrong about that