Harris' postwar despatch.
Looking closer at the original, I see the numbers on German guns/searchlights/etc. are based on intel reports -- so I think a grain of salt required.
The 1944 numbers for heavy AA guns are close to the mark - Harris has 11186, in reality there were about 11500. However, he has 9950 in March of 1945; Luftwaffe returns have about 12000 in February.
The discrepancy is larger in light AA guns Harris has 17508 in1944 and 11324 in 1945.
Here are Luftwaffe returns: 20mm single 19001 in 1944 - 10531 in 1945
20mm quad 2602(10408 barrels) - 3768 (15072 barrels)
37 mm 3358 - 4393
foreign production all calibers 2346 - 2510
in total: 35113 - 32506
These are just Luftwaffe numbers - you'd have to add Army and Navy numbers which in the case of 20mm weapons would be substantial. So Allied Intelligence severely underestimated light AA numbers. Low-level attacks against defended targets were by no means milk runs even in May of 1945, especially if you ran across 20mm quads with experienced crews. When the USAAF tried PTO tactics with A-26s against German targets, 12 of 12 were lost on the first attacks, mostly I think to light AA.