I've been personally wrestling with this. The answer for traditional reserve retirement: As a TR, if you retire with paperwork that says O-4, you get O-4 pay when you finally get it at age 60. My MFP troops were kind enough to show me that in writing...no idea the reg...to make sure the fight was worth fighting.
After being twice passed over, I pinned on O-5 shortly before separating for the AFRC (long story). Fast forward to me with 20 good years (a few years after joining the AFRC) and ARPC started claiming that my DOR was my accession date into the reserves, NOT my actual DOR when I pinned on while on AD. Our personnelists were entirely perplexed, but it turns out that they can't call ARPC directly. Yes, you read that correctly. There is no pipeline for base level AFRC personnelists (at least mine) to contact ARPC directly. They had to submit a trouble ticket, just like I did. They got the same answer I did: "you need 3 years TIG" with no reference or reg that states your DOR becomes your accession date.
Four months and much pain later: My personnelists finally found the AFI/AFMAN/REG that states with no break in service, you keep your original date of rank. POOF! Magically my retirement order is published to retire as an O-5 at my originally requested date. ARPC is a completely corrupt clown show run by GS's who will suckle at the teat until they literally die, all the while stating as "fact" what is actually "I think I remember from back in my day the reg said..."
Two UTA's left.