I’ve spotted something different in each of the two GNRI photos. The M1 van, (looks like 453), at Dungannon has had its lower beading renewed with flat strip instead of half round.
To the right of the image of K3, No.12, there is a K15. This is one of the first built, as it has a Truss Rod underframe, instead of the LMS style angle iron framing, which all later builds had.
Paul