No, I don't think there were half a million in 2010. I think you're misinterpreting what I wrote.
According to John Koskinen, former IRS commissioner, there were ~ 100,000 IRS employees when he first started working there. I don't know if that was in 2010 but if it was, 17% of 100,000 would be 17,000 less employees than when he started.
17,000 still would be pretty far from 87,000 ...however.... apparently the majority of the people still at the IRS are at or near retirement age. So they expect basically the entire workforce to be leaving in the coming years.
Also..... based on the fact that the IRS was only able to answer the phones 11% of the time in 2021, I would tend to think they are currently understaffed.
Not sure about 5 million rounds of ammo (?)