One thought is to highlight the change in radioactive element in the lume before they introduced the circle T
A couple of the issued watches of this age with changed lume had the Fat Arrow printed on them by the MOD
Although it could just be that this was the type of arrow was used at that particular time.
The Broad Arrow on the later Hamilton was different from both the 53 dials and then the lost navigator had another slightly different variant with a longer tail. If could just simply be that someone prefers the look of that style of arrow. - my money would be on the latter explanation.