Depends whether you are an Occifer or Airmen. Different rules apply. I can only tell you the airman bits.
PVR- Premature Voluntary Retirement. They decide how long the notice period is. Usually 12 months can be 18 months, sometimes less than 6 months. Up to PMA!
NGR - Notice of General Release. Whereby you give 18 months notice to leave.
PVR is a privilege.
NGR is a right.
As far as NCA flying pay is concerned, it's the same for both. You go down a band.
Resettlement rights and terminal leave are unaffected by both if you have passed the IPP point.
I believe, although do NOT know for sure, but if you are an Occifer and PVR it can affect your pension payable. Airmen’s pension rates and gratuities are unaffected by either method.
