Seeds from years gone by

The sunflowers are growing at great speed and will soon be ready for replanting at the allotment. We've been sowing seeds from packets dated a couple of years ago with variable success; leeks are doing really well with other plants the germination rates have been variable. We're also  sowing in batches a few weeks apart, so hopefully we will have lots of produce but not too many gluts - there's only so many courgettes you can get through before you never want to eat another one again in the whole of your life or at least the current season.