It shouldn’t be that hard to figure out given you have time and are confident you have accurate title.
Get the total unit acreage for each well from the NMOCD well file. Then figure out how much of your acreage was included in it. For example, 160-acre unit / 40 acres owned = 1/4. Now look at the lease. Assuming your royalty percentage is 1/8, and you owned 20% of the minerals under that acreage, your interest in the unit would be:
1/4 (from example above) x 1/8 (lease royalty) = 1/32 x 20% (your percentage ownership) = 1/160.
Using the numbers above, now look to the production data. If the well produced 10,000 barrels last year, at an average of $50/barrel (use historical WTI data for each year), then you would take 10,000 x $50 x 1/160 and that’s “roughly” what you would have received in royalties from that well, less any allowables for marketing, etc. Any allowables would be identified in your lease. Do this for each year and you have an idea of what you would have received from each well over that time. If you want a more precise figure, use the monthly average production and WTI historical figures.
I really hope this information helps, Don - and thank you for your service! Best of luck!