(1) When in doubt ……… throw it out.  If your string has picked up dirt / grime it’s in the wax and will act as an abrasive, eventually causing the string to fail.

(2) Learn to make your own endless loop strings.  Plenty of YouTube videos out there and after a couple of tries it gets pretty easy to spin one out.  Plus pride of craftmanship and all of that.

(3) Cheap advice; Set up a string, shoot it in, set nocking point, and then put it in a labeled Zip-Loc bag as a spare and then set up another string.  I was at a 3D shoot last summer and blew a string that I shouldn’t have been shooting in the first place. The compound shooters were all ‘Well, I guess you’re done for the day’.  It took all of three minutes to swap out the string and step up to the next stake.