Homestead owns the full 360-acre tract. All mineral interest. He/she has three kids. They now own 120 net acres. Each owns 120/360 (or 1/3 each). Then suppose each of those kids has three kids each. Then the first and second generation has passed away, or maybe only one of them. Each grandchild now owns 1/9 of the original 360 acres, which equates to 40 net mineral acres. Another way to think of this is like stock in a company. The shareholder owns a fractional share of the entire company.
Not all records are listed on OKCountyRecords. Some counties only go back to a certain date. Others go back to prior to statehood. Then some counties don’t list all the descriptions, or they have errors when inputting the information.