Generally, if you lease two tracts together, which your parents did in 1977, they are both held by production by a well on either tract. You would need to contact your operator to verify if that holds true for your lease since it was earlier in 1977. You could ask for a release of lease in 20 and see if they would do it.
Leasing agents do not always do a good title or production check, so mistakes can be made.
Mewbourne has filed for a location exception for a well in 20/29-15N-20W. I do not yet see a permit for Cow Hills. If you are open to lease, then you will probably be contacted. If you are held by the 1977 lease, then you will not be contacted and will still be able to get royalties from the new horizontal well at the previous lease rate.