Some long overdue updates!
I have discovered Great-Uncle Fred listed in the 1919 editions of the Absent Voters Lists. The entries not only give his regiment and service number, but also the date of his demobilisation.
However, far from making things clearer, this actually muddies the waters, for, while this has led me to find a medal card for an FS Jones with the same service number, the regiment is completely different.
I'm only partially certain that this is 'our' Fred Jones, as the AVLs could be quite inaccurate, and it could also be a huge coincidence, so as of yet proof is not conclusive. The information is presented on his page.
Regarding my Grandad, I have found a nice sketch of the lock at Landrecies, that the 9th Devonshires had to get past during the battle of the Sambre.