Looking at Fikira's extensive picture collection it seems the second number varies from 1 until 90's. I doubt it signifies the length of the razor.
Iwasaki
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Yes, that certainly does seem like proof that it does not always mean the length. But could it mean the length sometimes? I have 3 stamped Iwasakis. Here are two of them. Is this just a coincidence?
Second stamped number: 46
Second stamped number: 52
The third is stamped 71, though, which clearly does not match: