One thing about ferrocerium rods is that they will deteriorate with time/moisture if exposed. Notice that when you buy Ronson 'flints' for your lighter they are covered in red varnish. I would guess that this coating stops or slows the oxidation process. Scrape that off the first time you spark it and you start the clock.

I don't know if Sparklite flints are fully varnished when manufactured, but it's clear that if you spark it once to test it and put it back, it may fail some time in the future. The thing to do is have a few around, one to play/practice with and leave the others unsparked. And inspect your kit every so often.