I think throat rivets were around a bit longer, into 1949. Of course Heiser could have stopped producing them a bit earlier, but it took some time to use up stock. Unlikey it took two years to use existing stock for most models, so I believe they were produced a bit longer. I have seen several knives from the period that still had throat rivets, even a couple that were dated possibly into the new decade. One neat piece was a circa 1949 1-7, stag with fingergrips. The unique thing was the stag was not pinned!

I don't know if the switch from the harness rivet for the keeper to the smaller rivet as at the throat was anything more than expediency on Heiser's part.