The expansion of production achieved in 1944 did not at any time lead to a significant increase in Luftwaffe frontline strength. No fully satisfactory answer has yet been produced for this problem. A large number of Luftwaffe records were destroyed and many of the surviving ones have been difficult to decipher. With confidence, one can say that a significant proportion of the expanded production that did not turn up in frontline strength was destroyed at the factory, in transit, on operational airfields, or in combat. The sources agree, however, that attrition did not account for the whole of the problem. The balance might be accounted for, in part, by declining standards of record-keeping in the last year of the war. Another explanation favored by USSBS investigators was that certain officials, chiefly Karl-Otto Saur, the head of the special Fighter Staff under Albert Speer, were not above altering the books to make their production efforts look better than they really were.
The US Air Force noticed DURING THE WAR that they were shooting down large numbers of fighters, but the Germans were replacing them, and they didn’t know how they were doing it.
The US airforce was examining shot down German fighters DURING THE WAR to see how they were made. And that is when they discovered the gigantic forgings, motly magnesium, which made rapid manufacturing easier and cheaper.
Then they went into the captured factories DURING THE WAR looking for the forging presses that could produce such parts.
https://www.youtube.com/watch?v=iZ50nZU3oG8
This was engineering analysis, not some after the war legalistic stupidity on whose recoreds were accurate.