Hi Heather. Interior finishes and seat moquette patterns are indeed an absolute nightmare to research. It would seem that so many enthusiasts specialising in, writing accounts, publishing books etc., on the subject of rolling stock, have gone to great lengths detailing every single feature and peculiar design quirk of the exteriors - but never seem to pay any more than scant attention to interior finishes - if at all, that is!
I have spent thirty plus years trying to find out what fabrics were used, and when, for my own illustration work, usually with little success.
What I can be fairly sure of though, is that seat moquette was generally regarded to have a useful working life of up to twelve years. As far as British Railways were concerned, that meant at least twenty odd years before replacement?!
Another thing that I can positively reassure you, is that both BR Southern Region, and the Eastern (at least) still continued to re-order the original fabric designs (presumably on the basis of a "repairs and renewals" budget?) from the earlier companies! New fabrics tended to be initially reserved for nice, shiny, modern, capital expenditure projects?!
I fancy everything got a bit bonkers, where almost anything went, from the middle sixties onwards!
There are recorded instances where, during a particularly desperate shortage of material, some Southern, 4SUB units were upholstered in the classic London Transport bus moquette!
"Hold tight", "Any more fares please" and all that!
Be that, as it may, it is probably safe to say that pre (that absolutely awful, all consuming, all-over grey, corporate image) "Trojan" design, the "Chain link" and "Octopus" patterns were the most commonly applied.
On the Southern Region, "Candy Cane" (red version for smoking and green for non-smoking compartments) was used widely, and lasted into the blue era - albeit in a rather grim and extremely grimy state!
Hope this helps a bit?
Pete.
P.S. Was hoping to upload a couple of images, but encountered a problem. Will try again in the morning!