Hi Brett - I spent quite a while going through terminology used...

Hi Brett - I spent quite a while going through terminology used in the quarterlies and that in the FDA process. For me the main clue is that after accepting a Submission, the process takes one of two paths: Additional Information Request, which has not happened (this also stops the clock). The other path is an Interactive Review (which we know has happened, and that it means nothing major is wrong). Because CDX went down the Interactive Review path, they could not have gone through an Additional Information Request - impossible as per the process definition. In the Quarterlies, the term additional information is used, but not in the formal FDA sense. See this line from the September Quarterly:

As part of the process, the Company collaborated with the FDA and completed a second round submission of information and anticipates receiving 510(k) clearance for the Pulse in late 2022, in time for our participation and exhibition at the Consumer Electronics Show (CES) in Las Vegas in January, 2023.The above implies that CDX was hoping for a 3 month process. It also implies the Submission was completed, but not yet accepted at the time of writing.
In the December update, we learn the submission was accepted, so it was probably formally accepted in October (FDA must accept it within 14 days). This starts the 60 day clock, plus 30 days for approval.

From the December update:
The Company continued to make good progress during the quarter in relation to regulatory approvals required for the Pulse. FDA acknowledged their receipt of our application and has accepted it for review. We kicked off the interactive review process in Q4 where we are corresponding with the lead reviewer and providing additional information as requested.

As I see it, the application was resubmitted, and accepted in October, and thus should be used as corrected application date.