Jan Still estimates that 113,000 byf 42 Lugers were produced for the German Military and spanned the no suffix to the L-Block. Allowing 10,000 pistols each in the B through L Blocks, knowing the J-Block was unused, accounts for 100,000 pistols. The no suffix and A-Blocks were shared between the byf 41 and byf 42 chamber markings. So the 13,000 byf 42 Lugers in these two blocks seem pretty reasonable to me, give or take a few.
All, or nearly all, of the Lugers produced in the M and N Blocks were Portuguese or Bulgarian Contract Pistols!!