Didn't we need to send a copy of first TPS approval notice when we applied for extension? I think that a copy of the extension approval notice will be required similarly if there is another extension in 2018 and you are applying for it. So if you don't have the extension approval notice with you, better reach out to USCIS to inquire how to get it mailed to you again sooner rather than waiting till the 11th hour next year. GL.