I take it that you have the Alan Godfrey 1913 map?
http://www.alangodfreymaps.co.uk/caernarvon.htm Also presume you have the 1891 map from the Old Maps site?
http://www.old-maps.co.uk You can download the 1891 map and they also have some other issues there though you can only view in a small window on the screen - or buy copies from them. If you are looking for old buildings then you might find on the RCAHMW site - they used to have large scale maps there (I think they are still there) and a database of recorded sites.
http://www.rcahmw.gov.ukReply (Martin Briscoe 12/07/2008)