If we take the GTA view that the law is the law and nothing will deviate from that, regardless of any HOC instructions then we have the following:
Semi-auto rifled guns are prohibited (Section 5). Anyone in possession in 1997 is O.K.(not too sure why)
All semi-auto pistols sold since 1997 have been Section 5 so therefore both the owners and SELLERS have broken the law.
The law does not differentiate between pistols and rifles. It just states "Rifled guns"
HOC 68/97 doesn't infer that it only applies to guns owned at the time. If it did it should have said so. It's quite clear that they were trying to correct a wrong wording and were doing it with the HOC.