It depends on the counties. Tim Dowd provided a link to a service with Oklahoma deed records online that may or may not have coverage depending on the county. If there are a lot of documents you need to review, it may be cheaper to do it in person or pay a local landman to do it (someone who does it everyday can find it alot faster than a novice, for example). It’s hard to gauge without knowing the full extent of your situation. If you have several in one county, it may be cheaper to pay a landman to research them all vs paying to look at a bunch of documents that may not have the information you are looking for.
I think I discovered the problem. Spoke with the son of the geologist, who worked with my dad (landman) and another fellow who was the engineer at Patrick Petroleum in the 70’s and 80’s. Apparently Patrick recorded assignments to begin with but then switched to “awards” at later date. I was told many operators convey/honor the award when a lease is sold but others do not. Probably explains why my dad got revenue checks for leases in 2000 but why his name is not in the paydecks after the wells were sold. Not certain if any people have heard of this situation?