Thanks very much for the information. I'm new to fixing (was going to say 'toying with' but thought that may offend those with a more serious view of the activity) watches and really am only looking at repairing a Citizen Navihawk of apparent vintage "made in December of 1990, 2000, 2010, 2020". It gets hard trying to find references to glass sizes, shapes and what-not, even finding an original part number seems more difficult than it should be but sites like this and people like yourself really help. Unfortunately the references are pre 1971 so not pertinent, but I'll order a movement (C300) and glass from Cousins in the UK (unless there's a better option), replace the existing glass, measure and see if I can find an appropriate sapphire replacement.
Anyway thanks very much, I was doubtful this old thread would yield much but you've proven me wrong.