Most dacron mainsails are constructed with a boltrope at the luff to control the luff dimension. The boltrope is usually a twisted dacron rope in a sleeve and which eventually additively changes / shortens its dimension EACH time you raise the sail with *proper* hoist tension.
Boltrope 'shrinkage' becomes a MAJOR problem over time with dacron mainsails ... it causes the mainsail to become 'baggy', full draft, draft aft, and the sail with a 'hooked up leech' ---- boat heels aggressively, major 'weather helm', SLOW boat. Most sails, with still good 'cloth', are discarded because simply the boltrope has shrunken over time. I betcha 95% of all dacron mainsails are replaced because of this boltrope shrinkage.

Suggestion: when having a new mainsail made, ASK the sailmaker to add a 'stored' amount of extra length of (UV protected) luff boltrope on TOP of the headboard .... all ready and available to be slipped into the sleeve and the sail's luff dimension corrected and the sails shape 95% restored back to the OEM design shape. For DIY 'easing' of the boltrope, all you need is the OEM precise luff dimension, a sailmakers needle, waxed sail twine and knife: 1. measure the present luff length and compare to the OEM dimension that YOU measured when you bought the sail. 2. cut the sail twine thats binding the boltrope to its luff sleeve at near the head of the sail, and then 'slip' the stored extra boltrope into the sleeve to the proper correct length that YOU measured when you bought the sail, 3. Hand-resew the boltrope sail twine binding.

On my cruising boat, I 'ease my boltropes' typically at the end of each season of 'hard' sailing. Even if you dont do DIY sail adjustment, with a 'stored' extra length boltrope a sailmaker can 'correct' the sail's shape by 'easing' the boltrope in about an hour doing simple 'hand-work' ----- IF that extra length of boltrope is there and all-ready-to-go.
Note: sailmakers / lofts will usually NOT want to quote 'stored' boltrope on the headboard, as theyd sell probably 50% of the amount of new mainsails.

How to 'test' for a *shrunken* boltrope in a dacron mainsail (and also how to *properly raise* a boltroped dacron mainsail): http://forums.sbo.sailboatowners.com/showthread.php?t=120970