回複：OK to apply H1B with gap?

Up until today, BICE (Another half of the former INS, the other half became USCIS) does not release any stop-gap rules, so you have to keep valid non-immigrant status until the H1B start date. Otherwise, you may need to leave US and re-enter with H1B visa stamp in September.
It is not "duly filed" without the stop-gap measure if filing before OPT expiration but asking a H1B start date after OPT expired.