My very first grow failed but I had saved the remains of the print. It was B+ and by the time I had learned how to get threw the process, I wasn't so interested in that strain. Sat around for 6 years before I decided "why not". worked like a champ.
I have read of 20 year spores germinating just fine. Spores happen to be one of the hardest substances on earth. The longer they sit, the more a pre-hydration seems to help. I often make a syringe and use it right away with no foul results when using fresher prints (less than 6 months old). But you'll want to let it sit in the syringe a day or more as is typically recommended.