They were right too! As I mentioned on that thread,
So, the "1956 Ten Mile Road Map" we've had on SABRE Maps for years (that I knew Ritchie had arranged with the British Library that we could reuse) turned out to be one of the ultra-rare proof editions from 1955, from which the roads were updated to give us the "real" 1956 map.According to the relevant works, there was only one revision published in the 1950s (which was the 1956 revision as stated). But looking carefully at the source map for the SABRE Maps version against the NLS version shows a few subtle differences in the marginalia - the NLS's states Revision A, whereas ours has no letter code. Theirs has the copyright date of 1956, whereas ours says 1955.
There's a few other subtle differences - the A339 between Newbury and Basingstoke is shown as Trunk on the NLS's map, and not on ours. My personal copy of the map matches the NLS's.
To cut a long story short, it looks like the copy on SABRE Maps is actually one of the final proof editions from 1955...
So, following that revelation, that map has been moved to a more correct 1955 label, and the real 1956 revision A map has been scanned, georeferenced, tiled and now uploaded to SABRE Maps. I've now found quite a number of differences between the two maps other than those mentioned on that thread (such as the A457 and A4126 not being shown fully on the 1955 proof edition) - what else is there?