For citizens and nationals of El Salvador who are allowed to remain in the U.S. for a limited time under a grant of Temporary Protected Status (TPS), the current expiration date on their status is March 9, 2018.
When this latest TPS validity period was announced, U.S. Citizenship and Immigration Services (USCIS) automatically extended the validity of existing TPS-holders' employment authorization documents (EADs) through March 9, 2017. The purpose was in case USCIS got delayed in issuing actual new EADs holding the updated expiration date.
However, it appears that the agency is behind in approving that latest batch of EADs. Accordingly, it is automatically extending them all for an additional six months.
If you hold TPS from El Salvador (and have kept current by submitting your renewal applications) your EAD is now good through September 9, 2017.
Of course, showing your work permit card to your employer and to any government agencies or others who need to see evidence of your lawful status here might be less than convincing, given that it will show a long-passed expiration old date. USCIS advises you to also show them a copy of the relevant Federal Register notice announcing this automatic extension.