As Berny says, the bolt rope, being a "wound" rope, will, over time, tighten its windings and appear to "shrink", but instead of unstitching it, we have found that if you lay your sail out in the (sea) water with the battens loosened or out, until it is fully wet, especially the bolt rope, then run it up the mast with the boat on it's side, attach the luff tension system, stand the boat up and pull the luff tension down as far as you can (and then pull it lots more), let the sail dry out with the luff tension fully on. You will find then that the bolt rope has been “stretched” and set back to its original length, and not only will the sail go up and down easier but, your luff tension control on the water will be much more versatile.