If you look in the following:
Ordnance Survey maps : a descriptive manual by J.B. Harley
Publisher Southampton : Ordnance Survey, 1975
you'll find reproductions of legends of 1:2 500 and 1:10 560 maps. There
is a copy in your library, shelfmark: Q 912.42 (H).
Another useful book is:
Ordnance Survey maps : a concise guide for historians by Richard Oliver
Publisher London : Charles Close Society, 1993
Shelfmark: 912.42 (O).
I'm afraid I know nothing about variation in the legends over time, but I'm
sure there was some!
Hope this is of some help.
Antonio da Cruz (Tinho) [log in to unmask]
Map Curator, Department of Geography, Roxby Building
University of Liverpool, LIVERPOOL L69 7ZT
Telephone: 0151 794 2844 Fax: 0151 794 2866
See the British Archaeological Association web page