Just a head's up where we are with this.
The scans came from the National Library of Scotland - they date from 1920 - 1924. Some have up to 3 digit A roads, some have just the "first 99", some have draft number, some have no numbers at all.
This is without doubt the hardest and most time consuming project I've ever done for SABRE Maps, and having started (and given up) at least three times in the past 15 months I've finally got something working. Part of the problem is that, unlike OS Maps, there are no gridlines on 1920s Barts maps. There are mileage markers and lat / lon graticules, but they just aren't accurate enough to work properly. In the end I ended up writing an application to do the calibration and did each map by hand running off trig points, railway lines and roads I'm reasonably sure haven't changed course in the last 90 years (such as country lanes).
Finally, one of the biggest "head to desk" moments has been what's now called the "Burnley Black Hole" - a small part of what's now the M65 corridor that is near the join of 4 maps but actually appears on none of them at all. This is best illustrated with a picture, I think :
burnley black hole.png [ 392.27 KiB | Viewed 438 times ]
Anyway, touch wood there'll be something up over the weekend.