My parents visited us second time during their 10-year B2 visa. I just realized that my parents I-94 expired yesterday (on 07/06/2018), and they left the US on 07/07/2018. Is this considered an overstay? I'm planning to apply for another B2 visa sometime in December 2018, as their current 10 year visa is expiring on November 10, 2018. Thanks.