About three years ago I picked up a used Woodrup Giro Touring frame. Kind of a gold/champagne color with l-o-n-g wheelbase, 2 sets of H20 bosses, on top of BBKT cable routing and fully sloping fork crown. The frame had a 4-digit serial number of #4377. I spoke with Stephen Woodrup and he had records of serial numbers, but I don't know for how far back. Serial #4377 was built in 1980 according to their records.
He also told they were now exporting about 150 frames a year to America which was about 1/3 of their production at the time my frame was built. So, before the big lugged/steel market crash they were building about 450 frames a year. I picked up a second Woodrup Giro Touring exactly like the first one with a serial number of #4728. This frame was built in 1981 according to their records.
I bought yet a third Woodrup and this one is definitely a bit later with Reynolds 531ST tubing. It also has nice little reinforcement tabs around the bottle braze-ons. The serial number has changed to 5-digits on this frame (#84095). According to Tony Woodrup (son of Stephan and grandson of Maurice Woodrup), they changed from a 4-digit to a 5-digit serial number in 1982. And yes, the first two numbers of the 5-digit style numbers is the year of production...#84095 was built in 1984.
The long and short of all this is that frames built pre-1982 have a 4- digit serial number with no date code. The numbers just run in numerical order. Frames from 1982 on have a 5-digit serial number with the first two digits representing the date of production. Ok, hope that helps!
Jim Cole
Memphis, TN