Ahhh I see now…
The actual description will not change unless you liquidate or acquire more lands. As you point out - what could be inaccurate is the net mineral acreage stated. To use your example an “Undivided eighty 80 acre mineral interest” could be 40 acres (or less) now due to the split in title you referenced (or others in the past). It could be this description has been copied from a prior conveyance when 80 NMA was owned by your predecessor in title. This is very typical and would not surprise me.
Anymore, most use language along the lines of “an undivided MI in the…” to avoid creating confusion. Frankly when I come across stated NMA’s in a description I think to myself “that’s helpful - if it’s right” and usually end up making a note as to the conveyance doc purporting to convey XX amount when truly ZZ is owned.
Either way you clearly seem to be in title to a mineral interest. Determining the true proportion would require a title search all the way back to patent, IMO. This CAN be done by yourself - you’ll need some help and patience and be able to go to the Garvin County Clerk’s Office in Pauls Valley, or you could contact a landman or attorney. Typically an independent landman will charge $250+ per day for research and be aware most love to milk the clock. Best case you find a landman who is, or has been working this area.
Southern and Central OK are my front and back yard - I’m happy to refer you to the landmen I know or provide you some assistance along the way.