The IRS will know because the IRS is the federal tax authority that extended the time pay any federal taxes owed.
Go to this IRS website - San Diego area taxpayers impacted by severe storms, flooding qualify for tax relief; various deadlines postponed to June 17 - https://www.irs.gov/newsroom/irs-san-diego-area-taxpayers-impacted-by-severe-storms-flooding-qualify...
