Ruger's page for manufacturing dates is a little confusing. What they don't tell you in the year 1973 is that they finished shipping the last of their OM Supers that year and began at 81-00001 for the NM Super, going to an estimated 81-12400 for the year.
Then the general sn beginning in 1974 was 81-12401.
The front of the trigger on your gun is smooth?
Chet15