Space channel here is airing it on Thursday along with Prodigy and Discovery (add Ready Room on Youtube and was quite the Trek filled past day), so I finally watched episode 1. Did Gates say 9 series in the intro? I count 11, 12 counting the upcoming Strange New Worlds, 14 counting After Trek and Ready Room.
From watching the back half of the docu-series on History Vault I can explain the numbering somewhat. For one, they treat Prodigy as upcoming, not currently airing, so when this was finalized they must’ve thought it would be released before Prodigy’s premiere.
As for why they say 9 instead of 10, I’m guessing Gates & the documentarians weren’t including Short Treks, because they mention all the other series to date over the course of the Center Seat series.