Leftover seed can be a lot like those girls at closing time. You might get a winner. You might get hurtpeas.
I gave MO $42 for beans that were brand new and the RIGHT MATURITY when I planted. Year old beans that are not geared to be planted when and where I put them may or may not work out.
Beans are cheap fertilizer wise. Bargain for tonnage in areas where deer don't decimate them.
I got burned on my MDHA corn. It was free but it never dimpled and dried and the deer did not like it. Few hundred bucks in fertilizer went to waste on that plot. Disked half in this spring and saw one volunteer corn stalk this summer.