If there's a photo there ye go lads, that's the proof! If such things occurred, they didn't stay that way long copmpared with 141s and A's - although with a greater number of locos in each of those classes that might explain why they seemed more numerous.. Interesting re. 121's; again, while I never saw one myself, that's not proof it didn't happen! It would be interesting to see photos. Yes, they did tend to "slap the new logo on" - I suppose with the new IE logo similar will happen. It certainly did when flying snails gave way to broken wheels. Possibly more so on CIE buses, but I have seen a pic of a green double decker with a white broken wheel, and pics of both navy and cream double deckers, and red and cream single deckers, with white "snails".
Preserved NCC "WT" No. 4 ended NIR service with an NIR logo on one side and a UTA crest on the other........