Lost amid the federal government shutdown was the fact that the new fiscal year began on October 1. With that date thousands of H-1B workers began their H-1B status.
Those who obtained H-1B visas via overseas US Consulates and Embassies were eligible to enter the US, generally after September 20. People in the US in other status — e.g. F-1, Students; H-4, Derivative spouses — had their nonimmigrant status change by operation of law on October 1.
H-1B employers are reminded to update their Form I-9s to reflect these employees new H-1B nonimmigrant status. The USCIS increasingly is auditing companies I-9 files and issuing fines to the non-complaint. (Although one piece of good news from the shutdown: DOL investigations have been suspended.)