The expiration date is for internal uses only and doesn't concern you. What matters is the edition date, on the lower-left corner of each page. You have to make sure you are using an edition of the form that is still accepted at the time you file (the form's webpage on the USCIS website indicates which editions are currently accepted). As long as you file an edition that is accepted at the time you file, you don't have to worry about future changes to the form.