DO328 SOMEWHAT CONFUSED OVER PROCEDURAL ASPECTS OF PAST AND FUTURE APCH CLRNCS AND SOP'S AT PIT.

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TOLD TO INTERCEPT THE LOC FOR RWY 32 AT PIT. WE WERE ARRIVING VIA THE 'NESTO' ARR. WE WERE ACTUALLY TOLD TO DEPART NESTO ON A 290 DEG HDG AND I BELIEVE WE WERE FLOWN THROUGH THE FINAL ONCE. WE WERE APPROX 20 NM WHEN WE RECEIVED AN APCH CLRNC REFING 'WYLER' INTXN. WE WERE TOLD WE WERE '12 MI FROM WYLER; CROSS WYLER AT 4000 FT; CLRED ILS RWY 32.' AT THE TIME WE WERE ENCOUNTERING CONTINUOUS TURB AS WE WERE JUST IN THE BASES OF SOME CUMULUS CLOUDS. CITING THE APCH CLRNC; I DECIDED TO EXERCISE THE CLRNC TO CROSS 'WYLER AT 4000 FT' BY BEGINNING MY DSCNT EARLY IN SEARCH OF SMOOTH AIR BELOW THE CLOUDS. IT WAS CLR BELOW THEM. IT WAS LATER THAT I BECAME CONCERNED THAT MAYBE WE CROSSED 'GRUNZ' ON THE APCH TOO LOW. THE QUESTION IN MY MIND WAS DID GRUNZ EVEN MATTER TO US OPERATIONALLY. MY THOUGHTS WERE THIS: 1) GRUNZ WAS NOT MENTIONED IN THE APCH CLRNC; ONLY WYLER; 2) REF AIM 4-4-9(E) WHERE 'CROSS FIX AT...' ALLOWS A PLT DISCRETION DSCNT TO MEET THE RESTR; 3) REF 4-4-9(C) A DISCRETION DSCNT MAY BE BEGUN 'WHEN THE PLT WISHES.' 4) REF AIM 5-4-7(B) '(AFTER ESTABLISHED) PUBLISHED ALTS APPLY TO DSCNT WITHIN EACH (SEGMENT) UNLESS A DIFFERENT ALT IS ASSIGNED BY ATC.' CONSIDERING LCL KNOWLEDGE; I HAVE NO CONCERNS ABOUT THE SAFETY OF MY ACTIONS OR THAT IT IS UNCOMMON. I ALSO HAVE BEEN VECTORED AT 4000 FT TO 'WYLER' BEFORE. MY CONCERN IS PROCEDURAL. DO THE ABOVE CITED REFS ALLOW ME TO ACT AS I DID. OUR DSCNT WAS COMMENCED ONLY SLIGHTLY EARLY; HOWEVER AS A PROFESSIONAL I AM INTERESTED IN THE PROPER METHODS. THE AIM IS UNCLR; PARTICULARLY IN 5-4-7 WHETHER THE 'ASSIGNED ALT' (VERSUS PUBLISHED) CAN BE HIGHER OR LOWER. IT IS ALSO WORTH MENTIONING THAT WE WERE WITHIN THE CLASS B AT ALL TIMES; IE NOT BELOW IT. THE MAIN QUESTION IS; DOES THE CLRNC TO 'CROSS...' WHICH IMPLIES A PLT'S DISCRETION DSCNT; CONSTITUTE A NEWLY ASSIGNED ALT? FURTHER COMPLICATING MY CONFUSION IS THE FACT THAT THE MEA ON THE NESTO ARR IS 5000 FT.