Incidentally, I have been working on collecting Italvega and Torpado serial numbers, in order to assist with future dating. It had been my assertion that shorter 5 digit serial numbers take the first character from the last digit of the year in the 1970s that the bike was made, and ceased in 1971-2 with the introduction of a six digit series. I further believed the first numbered character of the 6 digit system to mean the same thing, beginning in 1972. However, the serial number on Otis' Ebay bike is 3505, which is shorter than most all others I have logged from that time period.
My undrilled Super Speciale has the serial number 3632 (or as I deemed, with a poorly stamped first character ... 13632). Because Super Speciale framesets from 1973 forward had the same drilled dropouts of the Superlights, and mine here does not have this feature, it is clear that mine was made prior to the introduction of the drilled models in 1973. Hence (contributing to my earlier model, 5 digit assessment theory), I believed my Super Speciale to be from 1971.
A different Superlight model (drilled) that I have here is stamped: *405538*, and yes, there is clearly one 5-pointed star before and after the six digits ... this is a repeating theme in all the 6 digit serial numbers I have logged. Following my system, I believed this frame to be a 1974 model, built in May (2nd and 3rd digits being: 05). All 6 digit series I have seen begin with a number from 2 to 4, and the subsequent two numbers (the 2nd and 3rd) always fall from 02 to 11, thus far. This is how I came to suspect that these numbers represent the month made.
There are a couple of other 4 digit series I have logged; one being 1047, and the other being 5848. I'll spare you all the comparisons I've made. however, although I'm still stumped on these, I believe them to be earlier models...
We know that the drilled SL and SS models came out in 73. At least one drilled SL model has the 6-digit system, and at least one undrilled SS model has the 4 or 5 digit system. Therefore, a yet unproved assessment came be made, that the shorter series predate the longer.