I have said this elsewhere, but there is a lack of appreciation that up to WWII the majority of rolling stock in use was actually of pre-grouping origin! This goes for wagons as well as carriages. In some cases railway company wagons were still running round in pre-grouping livery as late as 1933, ten years after the grouping. There were complaints when WWII was impending that British companies had invested far too little on modernising facilities since WWI, with the largest proportion of wagons in use remaining that of 10 Ton to 12 Ton capacity. The NE Area of the LNER had a larger proportion of 20 Ton Coal Hoppers than elsewhere but the investment in handling facilities for them was largely made by the NER prior to WWI. However, since many companies had struggled to even survive the trials of the 1920s and 30s it is not surprising that modernisation was a luxury which was afforded by a small minority.
Yes, containerisation was under way by the late 1930s but that traffic was dwarfed by coal traffic, which was still in the hands of wagons which, in some cases were exactly the same ones plying their trade twenty-five years earlier in 1914. Some even retaining their original grease axle boxes.
I have all four volumes of Hudson's Private Owner wagons and even if every example in all four volumes were built it would still only be a small fraction of those which existed. With many being built to RCH standards with RCH parts there is a case that "generic" wagons are exactly what the companies wanted. Wagons almost identical except for livery. The common user agreement of 1917 meant that most wagons from most companies could (and did) turn up hundreds of miles from home prior to WWII. I have shots of NER company wagons at Barmouth in 1924 and an LMS open wagon turning up in more than one shot of the Roseby branch in the 1920s. Getting up there meant an ascent up a 1 in 5 incline, so it was hardly just happenstance that it was up there. It may have stayed up there for some time. If I recall it correctly, in a census of LNER wagons towards the end of WWII there were several thousand wagons which had not been seen by the company since the day they were built!
Still, I would welcome Camscott turning his hand to some railway company wagons as used by pre-grouping companies. As ever, drawings and photographs will be key and we should not underestimate the costs associated with assembling that data. We should not just expect Camscott to somehow gather this together. If somebody has a particular company or particular wagon in mind, then at the very least they should provide Camscott with drawings. A photo would help him too.