I was curious to see how the STF expanded in the latest expansion (Shadowbringers). It's apparently been upgraded from 3 people to 4. These STF staff are still, apparently, all in Japan. One of those is the lead, so who knows if that person looks at reports as well. Their QA department (incl Game Testers) looks to have more than 60 people, so having a few more for the STF isn't unrealistic.

https://youtu.be/ZP3LiAik_-Q?t=1282