I have a few bikes, one is a very old Carlton. It has frame number NG5240985 It looks like it was made in Nottingham, in MAY it could be the 985 th frame. but what does the 5240 mean? The first number is said to mean the year (5) but is it 1975 or 1985? I think that post 1981 the carlton frames are said to have a W frame number not NG. Does anyone have further info please? It is a nice light bike with a racing style not touring. I need to know the value too if possible. Thanks!