I think applicants from other months are not actively updating their status (at least not as good as September 2020 applicants). I've removed several September 2020 applicants from the sheet because they were stale entries and weren't updated in a long time. I also check with applicants from time to time to get updates if the records haven't been updated. That is the reason why the September sheet appears to be complete and appears to have more test invites IMO.
I think at least one person from each month's thread should take up that responsibility of keeping the sheet complete and follow up with people with stale entries. Otherwise, the data is skewed and won't reflect the correct stats.
It is pain-staking work but at the end of the day, it shows the correct stats and the data isn't skewed so it is worth it.