I've made all of the corrections suggested to date, and the newest version of the map is here:
Note that it's now a jpeg file, and as a result it's quite muddy. It's a huge image and it's very heavily compressed, but hopefully it'll open more compatibly on everyone's computers.
There are still a few stations (particularly around Newcastle) that don't have opening or closing dates. If anyone has dates for these stations, if it's not too much trouble, I'd love to add them to the map.
The only thing remaining to finish is the information in the little boxes around the map. This is proving more of a challenge than it really should be, because I only have the internet as a source, and I'll be damned if I can find coherent opening dates and anything useful about the history of a lot of the lines, particularly the most often used ones! (Which also happen to be the ones with the longest and probably most interesting history!) In particular, I can find approximately bugger all about the Main North Line, the Main Western Line and the Main South Line beyond some very vague and confusing opening dates.
I'm wondering if it would be better to provide a lengthier description for closed lines, and leave the current lines at simply opening and electrification dates, and no history? Even finding the opening dates for most of the lines is more of a hassle than it needs to be, as most of the sources online conflict wildly.
Alternatively, I could remove the information boxes for the current lines entirely and just provide a legend to explain their colours, leaving only the infoboxes for disused lines. The legend could also explain the industrial/racecourse/mortuary/airport symbols for those unable to figure them out for themselves.
Anyhow, feedback is greatly appreciated. Corrections, also. For the moment, I'm fairly confident that all of the disused lines have been appropriately represented. So, unless I've managed to omit something ridiculously huge and obvious, I'm done debating lines, and they're staying as-is.
Thanks for all your help with this map. When it's finally finished and credit is made to everyone who's provided information and the appropriate sources, I'll ideally be able to make a printed version available at a reasonable price to anyone who's interested.