For me it's just parsnips that I would always use fresh seed for as far as "conventional" veg goes. I find with parsley warmth and patience is the key to get it to germinate.
For smaller seeds e.g. lettuce, beetroot, spring onions, carrots, just sow more thickly to take into account any reduced germination rate.
I tend to chit larger seeds anyway (see separate thread) so you quickly get an idea of viability. You could always try this now on any you are concerned about. That would give you plenty of time to purchase replacements if necessary.
