I have 220 hours on a IVO IFA ultra light 912UL over the last 2 years. Initially it required retorquing(sp)every 10 hours or so until the blades settled in to the grooves. I have had it off twice in order to replace the carrier pinion and I always retorque a few times after replacing. Be sure to keep the same blade,crush plate positions.
So far it has been no problem. I store the a/c in a hanger and this area is quite dry. I would be interested if these blades have a "best before date" though.
Cheers
Don