It's late. Do you know where your PC boards are? Let me rephrase that: Can unused PC boards be stored for future use?
Yes, they can - if stored properly. Keep them wrapped up, or sealed in a bag. Anti-static isn't necessary in this case, but it won't hurt. Keep them in a cool, dark place. Keep them clean. Do your best to avoid dropping them on the floor and stepping on them.
The board in this photo was left out on a desk for a while, and then shoved into a desk drawer. The environment took its toll on the immersion sliver finish, making it very much unusable.
What can go wrong:
#1: Fingerprints: The oils on your finger can etch your fingerprints into ENIG or immersion silver PC board surfaces. If you plan on committing a crime, go ahead and do this so we can catch you. If you aren't going to start a life of crime, be careful to not get your fingerprints on the board surface. Handle on the edges, or at least, don't touch any exposed metal.
#2: Moisture: Moisture is good for your skin, but not for your PC boards. Over time, PCBs can absorb moisture, especially in a humid location, or the ocean. If thrown into a reflow oven, they then might laminate. Do your best to store boards in a dry environment. If stored for a long time, you may want to pre-bake them prior to use.
#3: Atmosphere: Sometimes dirty air can contribute to tarnish or corrosion on the exposed land pads. Dust can settle onto the boards as well. Tarnish and dust can usually be cleaned off, but corrosion can't. Wrap up your boards for long-term storage.
Treat your boards well and you can likely use them at a later date. Don't treat them well and you may need to replace them, wasting a bunch of money. Often, the damage isn't as clear as in the above photo, but could still lead to poor solderability.
Don't surf on your silver