Some of them were certainly used by the engineers, whether they were painted black or not I'm not so sure. My memory of engineer's stock was that they were not repainted very often, and for old cascaded stock this meant that they were almost never repainted. The last of these coaches were withdrawn around 1950. There are photos of some in service in 1949 when they were over 50 years old. So that most of these coaches were withdrawn by the LNER and would have been given 9xxxxx number and painted oxford blue. Any that were withdrawn by BR were given DE 32xxxx and painted black. These is a problem here, in that I'm not at all sure what colour engineers coaches were painted during the 40s. I would expect that they were painted blue until stocks of paint ran out and then they were probably painted black, or brown, I just can't tell from black and white photos. If anyone has any information on this I would like hear it.
And on a related note, does anyone know how oxford blue weathered?