Do landmen ever get ownership wrong?

I purchased 20 acres of land south of Hobbs, NM in 2001 for ~$2500. I was under no illusions that I had any mineral rights at that price and after talking to previous owner about how most mineral rights in the area had been separated decades ago. I have owned and paid the taxes for the last 18 years.

I recently got an offer to buy my land for $40,000 and decided to see what had caused the significant increase in my land value as tax appraisal is still like $3500, and I thought maybe check things out if I wanted to sell or not.I have got a few offers to buy over the years, most are less than $5000.

I was researching back my deed since I was thinking of possibly selling. I found that my ownership comes via a Property Tax Div deed from 1989, which I believe is from someone losing the land for not paying property taxes. I was having trouble finding the ownership previous to that online.

So I went back to the original land grant in 1913 and went forward. I followed it forward to a man that bought it in 1929 via a warranty deed. Each transfer prior was by warranty deed also. Then while searching I found no more deed transfers or mineral deeds on that land from that person. I also saw the man and his wife had active oil and gas leases on the land till 1983 with the final oil & gas lease release in 1988.Then there was a big gap from 1988-2004 where there were no oil and gas leases on the land.

I later look and find out that the children of that man and wife have oil and gas leases on the property since I have owned it. There is no well on my land though.

I would assume the County would have taken ALL rights of the family when they took the property in taxes.

Now I am not claiming that I own the mineral rights.Only that I cannot see how the children of the people that lost their land to taxes could be rightful mineral owners. It was just some guy leasing their rights initially, not a big oil company.

There was a probate for the man in 1980, but from my reading it sounds like previously severed mineral rights can be assigned in probate, but cannot be severed during the probate without a deed being recorded, but I may be off hereā€¦

Could the landman who did the work for the original lease for the children really have missed the whole tax thing or is there something different about NM law related to tax liens and all.