Also mail each year in a separate envelope. So if you are filing state tax returns, you will be mailing four separate envelopes: 2020 federal, 2020 state, 2021 federal, and 2021 state.
Federal refunds are forfeited three years after the due date of the tax return. So, for example, your 2020 tax return was due April 15, 2021. In order to get the refund you have to file your 2020 tax return by April 15, 2024. Most states follow the same three-year rule, but some states might have a shorter or longer window.
Your tax return is the form you send to the government that shows your income and calculates your tax. The money that the government sends back to you is your refund. You don't receive your return, you receive your refund. The government receives your return when you file it.
