What do you have to loose by planting it? A couple of hours? Possibility of an 80% germination rate instead of 90%. You are going to have to plan for a couple of season any way to get the coverage you want.

What will it cost you to throw it away? Will your trash company take it? How much is the tipping fee a the Dump if you take it there.

What do you have to loose by planting it? A couple of hours?

No... a year. My concern is that I sow it and wait 2-3 weeks, then it's too cold to sow new. So I'm stuck with a mudpit until next year.

Possibility of an 80% germination rate instead of 90%.

If that's what you think I should expect, great! :-) I'm find with 80%, I was more concerned with 0%.

What will it cost you to throw it away?

Technically, about $400 to buy new.

Turf grass seed will remain viable for 2-3 years. The germination rate will decline but only by about 10-20% per year. You compensate for that by applying at a slightly heavier rate than suggested.

If you need to, you can dormant seed and the grass will germinate whenever temperatures are suitable.

Yes - still good.

See several discussions of this topic at thelawnforum website.

For example:

https://www.thelawnforum.com/threads/old-seed.1057/