The use of peel ply is to enhance secondary bonding,however if you are reinforcing an existing substrate you would have no need for peel ply as the surface is already established so you would put your new kevlar/carbon etc. on over the old surface that why the surface must be free of paint ,roughed up with sandpaper and cleaned with solvent before laminating then do all your lams at once. Peel ply is used between layers when you debulk the initial layers of reinforcement and subsequent layers /cores would be applied in a seperate operation or if you were bonding anothe piece of structure /brackets etc.secondarily.
Dave Craddock