I toss old seed as I go through it. Certain seed I always buy every year - spinach, carrots, onions, and corn. Each of these are important crops to me and their seed is often short lived. It would probably germinate the next year, but there is enough of a chance of a germination issue that I don't want to risk it. And especially with the three that I direct seed if it doesn't germinate on the first try it could limit my harvest. Especially with something like carrots. The spring crop is sown early and can take up to three weeks to germinate. If a batch doesn't come up I won't know there is an issue until way too late. I can't wait another couple of weeks as my rotations won't work out anymore. With spinach the earlier it gets up in the spring the better the crop. Because once May 15th hits they start thinking about bolting no matter how long they have been in the ground.
Now I have a sheet of paper - well two sheets - that tells me what I need to order and probably from who. I haven't ordered yet but I'll go over it once more with my garden map out and make sure I've got everything covered. Dreaming about next year is always one of the great pleasures of gardening. All the fun and none of the work. In my mind's eye everything grows well and the earwigs are nonexistent.