Not necessarily. I've been told by XTO that the name of one mineral owner in each tract is "randomly" selected and shown on the P-12. We have several family members splitting minerals acquired by my great-grandfather in the late 1920's and in some instances none of us have shown on the P-12's because they've selected other mineral owners and in one case my deceased brother was shown. We do not own surface acreage.
I've been told that if you're leased with the O&G company drilling the well or verify that your lease was acquired by that company, you're in the unit. I've been able to verify inclusion with O&G companies when we weren't on the P-12, just to make sure.