Can peat pellets go bad in 6 months if they dry out?

No the peat won't go bad, but you risk fungal diseases if you keep the lid on and this may also explain why growth has been slow, as seeds need good oxygen exchange to grow, something that is greatly reduced inside "humidity domes". Cannabis does not need humidity domes, it is not a rainforest plant.

Just like NobodysBuds said dried goods last way longer. I have used really old peat pucks and have had no issues, I also suspect some of the stuff at stores is also very old as well. with out all three, water, food and energy/heat, not much can happen. Good Luck!

Peat pellets wont go bad. They can hold too much moisture for a seed. This can cause root issues. You should soak them for 15 min then let them drain off some of the excess water before planting a seed in them. Even put them on a paper towel to wick out some moisture. Best of luck on your grow.

when i've looked up shelf life of things like promix, which is just sphagnum peat moss with some perlite and some ph-balancing components, they say 6 months. molds and such can build up... if it's been completely dry, that is different. Nothing is growing on it when bone-dry. As long as it was 'clean' before, there's a good chance it is clean now. The promix bales aren't dried out.. so opportunistic microbes would definitely colonize it if there are any resources to be had. inspect them, and see what happens... in the end, they are cheap, just buy more if there is any suspicion (not worth risk to save couple dolars). or, just fill that tray up with some coco/perlite (components you likely already have from diary info). will work just as well, if not better in many contexts.