In the real world UPS would not let you start you paperwork more than 90 days ahead of your projected retirement date and world sit on the paperwork until the last 30 days making it impossible to have any mistakes corrected early. Which is why there is a 5 month period after you retire to correct errors.
If you send in your paperwork earlier they would just sit on them or refuse to accept them that early.
One possible work around is to set a tentative date sooner than you really plan to retire so the paperwork will get started, then move the actual retirement date to later (which you are allowed to do).