Uncle,
I am very certain of my facts, as are Manning. The JSP remains extant and if you manage to leave before the 5 year point (say via admin discharge) then the rules prescribed still apply.
However, to be accepted on to PAS (RAF) you have to sign a ROS that effectively surrenders your 'PVR rights' as has been described in this thread. This is the relatively new bit that sits between the JSP and your acceptance (or otherwise) of PATOS.
Back in the day once an offer was given it could not be withdrawn and if you had the offer at 'first look' you had a period of years to make your final choice. You now have to accept or decline within a couple of months (although Manning have applied a little flexibility with this last bit for some special cases).