Fireworks are good for up to 10 years after manufacturing. Assume minus 1-2years by the time you have purchased them. This leaves you with a good few years to hold onto them for future events.
Just make sure that your items are properly store and have not experience moisture damage. Water damage can affect the quality of the powder in the item and the stability of the inner tubes. This can include too much moisture.
Items should be stored in a dry, cool place; preferably locked up or secured away from children. Storing in a non-heated building over winter is perfectly fine, just keep them dry.
If you are unsure of the condition of an item, use caution or do not use at all.
If you have old fireworks, multi-shot fireworks that did not all shoot, flares, squibs and or other explosives. You can call ahead of time and set up a drop off. 204-943-3332 ext.1
Not sure if your explosives are bad? call to find out.