been on the same bar and lines for almost 2 years. Outlasted 3 kites. Never had one cm stretch. And I ride hard. bridal snapped and pulled way off center etc, no stretching. Even had a knot in one line for 1.5 years.. nothing wrong with them.
It's a SS bar/lines (2010/11)
Came with Octane (dead), rode with old eclipse (dead) now with new Evo. Lines even, as new.
No idea how you stretch your lines that much.
My slingshot lines never stretched either. I've had 2012 switchblades about. 3 months and I've already adjusted the center lines twice.