I just returned home and now have access to my Kuhnhausen SAA Manual. He states 2nd gen s/n in 1975 ran from 70,501SA to 73,319SA. Then there is a note which says:
73,319 2nd generaton SAA's were produced. Although Colt 2nd generation SAA frame serial numbers ran through 73,319SA, the last 200 to 300 2nd generation SAA revolvers were assembled after production ended in 1975. Most of the revolvers in this last group were assembled with 3rd generation type SAA cylinders and hands. For this reason, many collectors consider 2nd generation SAA production to have actually ended at s/n 73,000SA.
Hope that helps.