Yes, the consists seem to have been somewhat random, but that's actually a very interesting feature of the early 1960s, appropriate given the planned launch of a model 121 in grey and yellow.
Elderly six wheel coaches or brakes mingled with laminates of various types, wooden bogies of GSWR* origin, and new Park Royals and "tin vans". Green, black'n'tan and unpainted dirty aluminium mingled as well.
Branch lines sometimes did have a tin van at either end of even a short conduct. I would guess that what my dad saw was the two coaches with a tin van at either end, though I recall a picture of a Ballina train with two tin vans at one end; another in the late sixties with a laminate or two followed by a then new BR van, and THAT followed by a tin van!
Nowadays, the standard consists of identical stock are just plain boring!
* By the 1960s, a "cull" had taken place of older wooden stock. Most surviving DSER stock had gone, and what was left of Midland stuff was mostly the hardy standard six wheelers. Curiously, most GSWR six wheelers had gone, and almost all DSER ones! West Cork retained just two or three ex Bandon coaches, mostly for Courtmacsherry excursions because they were of short length.