FishPaper rings are not a 100% necessity on the P42A cell.
The Molicell cells are designed with an abrasion resistant insulator ring on positive side under the wrap, making the pack assembly easier and safer for manufacturers. (This can be seen in black below)
Yes sure you can fit an additional one if you are unsure if your cell features these, but its not always needed for well designed packs built with P42A.
Anyways battery construction techniques is a little off topic here. If you’d like to discuss this further lets take it to one of the many battery construction threads.
(EDIT; i updated some of the langue here to be clearer with my views. there’s more discussion on this continued here The battery builders club - #19107 by ShutterShock)