The 15 day "Eligibility" rule is for UIL events only. Your link in blue even states "UIL Eligibilty". UIL governs only UIL extracurriculars, not all extracurriculars.

NP/NP "Eligibility" is state law and has nothing to do with UIL governance.

Region/All-State process is TMEA, therefore, governed by TMEA rules. TMEA follows NP/NP because of state law not UIL. TMEA will decide what the student in question will be able to do, not UIL.