Kavod Harav
Can I use an unopened box of machine Matzah from 3 years ago?
Thanks
Chag Kasher V’sameach
Yes, if its Kosher for Pesach matzah.
Can use for mitzvah?
Why not?
Is your question because 3 year old matza is stale?
This is relevant after pesach, when matzoh goes on sale, can you buy it then for the next year? Is last year’s matzah considered to be leShem mitzvah for the next year?
Is it leshem mitzvah if it’s from a different year?
The lishma does not expire. Meaning if the intention was good it remains good.