When bunches of surplus Hi powers were being imported, some were seen with non-matching slides and frames. Whether slides and frames were changed around by armorers associated with entities in the countries of origin, or by importers, I don't pretend to know. I suspect some of both. The pistol in question might be one of those with a later frame and earlier slide for some unknown reason. I saw all kinds of combinations, including some with crudely "force matched" serial numbers on slides and frames, on auction sites a few years ago.....