I think the crystals should be fine. They may have gained or lost a trace of water, but not enough to make any difference to the bees.
After making up into syrup, the solution does not store for very long at all. (And the sugar gives brown and bee-toxic HMF.)
If you need to store syrup solution for a couple of weeks, store it in the fridge - with a hazard label that is UNMISSABLE-!!!
Unsealed, it could be affected by water (which would affect the weight accuracy) and as already said, made into a solution with sugar there is the risk of forming HMF. As it is, I would trust freshly made solution from these crystals more than I would a bought in solution that has been sitting around in a warehouse or on a retail shelf for months.
Food has to have a date, and pharmaceuticals, but this may be only for stock control purposes. There's a use by date on the salt in my kitchen. It has been salt for over 200 million years since it crystallised from seawater. If I don't use it, it will still be salt long after the kitchen has disappeared.