The one thing I don't see mentioned is that these were not your normal bicycle. These were made, designed, and meant to be used as a tool for business. Not the recreational "toy" for a kid. I agree with the fact that the braces weren't given a lot of thought as to "matching" and think that the flat braces were used until they ran out and then switched over to the "rounded" ones. I have four pre-war ones here (and had a couple of other ones previously) and at least one of the still present ones has the half-round braces on the front (and there is no clearance issue) - BUT - I think they were switched onto the bike along with the front fender as it didn't appear to have been the one that originally came on the bike and the brace was installed with screws and nuts. The first one (18" framed '39 CT1) had flat ones on both ends.
On the later model (post war) where the stand was not mounted on the axle, clearance was a non-issue.
REC