You've learned probably the most important storage concern...……...humidity. You don't give any indication where you're located for folks to understand how big a concern that might be for your location, so no help there. But let me throw some thought provokers.
Most folks are going to buy their pellets "as needed" from a local store; big box, specialty, farm supply, hardware, Amazon, etc. I haven't looked over my bags to see if there's a "packaged on" date, likely isn't, so have no idea how long that bag has been bouncing around the world before it got to me. It's probably safe to assume that various storage warehouses, and trucking companies don't give an iota of thought to how they handle the pallet loads of pellets in their immediate care. For all we know, that bag of pellets we fret over sat on a dock for a week while Monsoon Mary did her thing a few feet away. Even in the warehouse, how long has it sat there? Do they follow a LIFO or FIFO policy for stock turnover, and does Charlie the forklift gorilla follow it anyway? How quickly does the store you buy it from turn over their inventory? Probably has a seasonal factor in that as well. I could go on with other variables like these, but will wrap instead. Presumably by ordering directly from the supplier/marketer/maybe manufacturer you're getting the "youngest" batch of pellets available. Same age and "life" experiences as a sack buried in a pile on a pallet that will be headed out to a retailer to maybe not be purchased for a couple years given the above possibilities. From that standpoint, whatever your personal storage situations, you'll likely take better care of those multiple bags than all those other possible people who would be involved. Well............….unless the stuff you buy from the supplier are returns from "the world".........….life can be so uncertain.