To go back to the original post, it's theoretically possible, of course, that a brown van might have ended up somewhere unusual, but it would be an exception, a one-off. Immediately after the GNR was split up in 1958, a GNR coach, still in brown, ended up for a very short time on - of all places - the West Cork system.
I have a photo of a DSER goods van in a siding at Achill, and I saw a pic once of a CIE wagon in a train on the Larne line in the early 1960s.