It occurs to me that there are probably a number of things that indicate dates with some reliability ( in the absence of serial number lists). They are:
Headbadge design (This seems to have changed at least three times)
Lug design (Anybody have any ideas about this??)
Componants used. (less reliable but still useful. When did Weinmann Vanquer brake models change, and when did labels switch from red to black, for inatance. I have found out that the centrepull 999 was first used in the UK in 1959 and not replaced by Dawes until the 80s ).
Comments chaps?