Voting by Mail
Harris County Mail Ballots Require a Fresh Application
Not everyone can vote by mail in Texas. You qualify in Harris County if you will be 65 or older on Election Day, are sick or disabled, expect to give birth right around Election Day, will be out of the county during the voting period, or are confined in jail or civil commitment but still eligible to vote.
A big one to remember: a past application does not roll over forever. State law (Senate Bill 1) requires voters to request an application on an annual basis. You can ask for ballots for all of a year's elections or just one specific election.
The most common reason a mail-ballot application gets rejected is a mismatched ID. Your form must include your Texas driver license number, Texas personal ID number, Election Identification Certificate number, or the last four digits of your Social Security number — and ideally the same one already on your voter record. Check HarrisVotes.com for the current deadline before you mail it.
Source to confirm: Harris Votes - Mail Ballot FAQ