The standard published reference shows the following production numbers and years:
1970-'71 - 41000 (this may indicate two full years' production)
1972-'73 - 30000
1973-'74 - 60000
The reference also states A1753xx was probably made in 1972, but for an age determination the sales or ship date is official. My guess would be 1973 based on this. A letter of authenticity would be the only way to get its official age:
Letter Process – Smith & Wesson Historical Foundation