5 digits should indicate 1955 to 64, which no one has deciphered an exact pattern, and even the published attempt is flawed, but it most likely indicates they were running out of 5 digits, using letters for sequence, changing the system every few years, and possibly different systems between different factories.
First letter in the 70s system was always factory, and on that later known system D is Ireland
W as a second letter is weird, definitely doesn't mean Worksop (Carlton), could be a month code, but probably simply using the letter in sequence as they did in the late 50s, RA, RB.
My guess on the bike above, falls between 60 and 63.
This example is known 1957 Nottingham.
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