Ed,
You and I go back a long time and there is not much written about the 10000 serial numbered guns or the 1 numbered guns.
I used to also believe serial ranges ran to 9999 but for a large factory making guns in 9999 ranges and randomly stamping a 1 in front does not make much sense?
It is more logical to believe 0000 is not a serial number so 10000 is a block number. No 0000 guns have ever turned up but the stamping machines went to 0000 when they turned over.
10000 lot guns are easier to keep track of, the Germans were meticulous about records and adding a 1 randomly doesn't make sense.
So that is all I have but I think the evidence is clear here ... 1 serial numbers as rare as 10000 and I firmly believe they were made in 10000 lot blocks
Mark