It strikes me that there is another solution yet for the jib stay sagging off to leeward (especially when the jib is on a furler) and therefore affecting pointing ability. That is not one backstay, but two---running backstays. Before you collapse into your monitor in laughter (thus damaging the thing and causing a repair bill that will set the repair schedule on _Redwing_ back a month), I will agree with you that an original equipment backstay or on older boats Jerry's backstay kit is the best solution for P-19's with the tall rig.
But what about the P-19's with the short rig--I seem to remember that the boom on the short rig is longer and actually hangs out over the stern. A fixed backstay wouldn't work if the boom extended out over the stern, but running backstays would, and they would give the mast the extra stability that it needs. It would also pull back enough to keep the jib luff tighter. Admittedly, it would work at the expense of setting and releasing the windward running backstay at each tack.
I have another boat (in addition to my Potter) that didn't come with a backstay because there was no room for one, and that had quite a problem with the jib (on its furler) hanging off to leeward. Running backstays have not solved the problem totally, but they certainly helped. And for those of us who are a bit gadget-happy anyway, there is another string to pull.
Regards
Tom Grimes
P-14 #363 Far Horizon
Muncie, Indiana