It wasn't to do with mounting lugs, more the fact that Pressac dropped a bollock on the size of the back plate full stop (their field testing is useless, we discovered the issue as soon as they arrived!). Even without ANY mounting lugs it wouldn't fit. An "adaptor" plate was released which was nothing more than a 2mm spacer. The Mk2 socket ended up even thicker than the old NTE5A's when it was re-tooled! It was only an issue if the metal back box was 100% flush with the finished surface...which most are! It obviously also affected dry lining boxes.
Mk1, MK2 & old NTE5A....