Charles Young suggests Speedwell serial numbers can be interpreted as:
month/year/Nth bike produced that month,
i.e., PR1273008 would be December 1973, 8th bike produced that month.
Updated 10.11.20

Owner Serial number
Steve Bauserman  17307
Charles Young  Pictures 173010
 Ken Wallace  1273008
Stefan Schaefter of Speedbicycles 1174016
Alexander March 1074014
Dylan Day 1175021
Carsten Rehbein Pictures 576014
Stefan Schaefter 67706

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