Sorry for the delaying in responding to the point about how the PVR table is used - but I hope the following is useful.
Let's say you have 18 yrs on AFPS 75 and another 8 on AFPS 15, at which point you are PVRing. Your AFPS 75 benefits will be calculated on your rank for pension and using the Pension Code table in operation at the time you leave.
They will look at the 26 yr PVR rate and your pension will be based on 18/26ths of that rate. So, effectively, you are building up time against the 'break even' point where Compulsory and PVR tables merge.