Both the wartime and post-war P.38's were called (and marked) just that, with the period (indicating the abbreviation for "pistole"), not a dash. The post-war Bundeswehr dropped the period in weapon designations, so the P1 is written just that way, with no period or dash.
Most of the P1 pistols seen here years ago were part of a production overrun; those seen recently were sold off. Originally, the post-war P.38 was made for commercial sale. The P1, as indicated by its designation, was made for the (then-West) German army.