What is the shelf life of new golf ball today?
From the Sarasota Tribune 12-6-03

Most new golf balls have a solid core with a durable cover. It is almost impossible to knock them out of round. The shine may wear off after awhile but it shouldn't affect the performance. The shelf life is infinite.

If you are retrieving golf balls from the course ponds, there's no telling how much life has been zapped from the ball. The newer balls will hold up better than the older, wounded balls, but if they sit in the water too long, the performance will probably be affected. If you are using one of these pond balls and it doesn't seem to fly the way you think it should, take it out of play.