If you researched all instruments filed by your legal description (not just searching by name) and revealed no additional instruments, then it is possible a mineral title search would not reveal anything different than what you already found. So if good research is already done (PXP telling you and your neighbors it is yours means they should have their own mineral title opinion for your property), then obtaining a mineral title search is probably useless at this point.
Besides, if the developer REALLY had title, wouldn’t they have produced documentation of good title to PXP so as not to lose their income? Considering the amount of money at stake, I’m pretty sure they would have fought the battle with PXP to prove ownership by now, if they had any credible documentation to prove they rightfully own the minerals. In this case I believe that answers any question about what “could” arise from a mineral search. If there were any aces to play in this game, the developer would have used them by now.