Amending a client's 2021 tax return within the amendment deadline, but the e-file season was closed, and the submission failed.  Then I found the 2 year e-file deadline.  Now we're printing and mailing.  but it could've helped if I knew that yesterday before trying to e-file.  All indications in ProConnect Tax were allowing the e-file, and it used one of my filing credits, so the system thinks it's been e-filed.