I know it's over 18 months since you originally posted this enquiry. But as I have a complete set of brass threepences, I checked out what you said. I have three 1937 examples. One as part of my collection, and two previous fillers, which I retained in a box. The one in my collection shows the B of "BR" level with the corner, as in the second example in your pic. Interestingly, of the two fillers, one is like your first example, and the other, actually has the B a little to the left of the corner angle. From 1949 to 1952, the BR is in a different place anyway, as the "Ind Imp" was dropped. But in the 1938 to 1948 inclusive, examples, the B starts directly adjacent to the corner.