Since now I have found such 7-digit 43-86mm zoom lenses with the following serial numbers (15 lenses, 10 of them in my collection): 4400001, 4400371, 4400471, 4400551, 4400751, 4400851, 4400901, 4401171, 4401281, 4401621, 4401681, 4402171, 4402281, 4402331, 4402851.
Notice: All theese serial numbers are ending by the digit 1!
My guess: the error happened at the very beginning of the 440000 serial number range and number 4400001 (instead of 440001) would be the very first misnumbered lens. The correct number of 4400371 would be 440037, 4402171 would be 440217 and so on. Conclusion: less than 300 lenses came out of the factory with a 7-digit serial number instead of the normal 6-digit serial number.
