Use the primers to amplify some samples that have already worked and see if the results look the same

Running the primers on gel will be a waste, plus it doesnt tell you whether the primers are still working or not. Try amplifying with samples to see if they are still functional. Lyophilized form should be fine, i'd left lyophilized primers at room temp for 2 weeks and they are still functional after diluted.

If you have lyophilized primers then you didn't have to worry about it. Because you can store lyophilized primers at room temperature also.

Wishes,

Mohinder