The Courtaulds wagons were not private owner - they were UTA's, mostly ex NCC.
Rather than being fully rebuilt, I'd say they were substantially patched up. They still had their NCC 1920s wagon plates on them well after withdrawal anyway! My own recollections of them were of wagons that were the FAR FAR from new looking.
After the Courtaulds traffic stopped, the vast majority were broken very quickly, with maybe a dozen or so retained for PW. And these lasted into NIR days when some more were broken, or set aside, others cut down and repainted with a single coat of poor quality emulsiony light grey paint. Naturally, the red showed through quite soon, and the metal parts simply returned to bare rust with tiny occasional patches of rust-stained grey!