I don't know for certain.
City's tickets are sold online so I log in with my username and password and flick through the available blocks, and estimate the numbers left. That gives an estimate for the numbers available online. If City don't put them online then my estimate will be wrong. For example, I know there are single seats left in Levels one and two that are not shown online so I kept my comment simple, "there are ~2,500 seats left online". There's probably a few hundred single seats left in a few blocks in Levels 1 and 2 that will become available as the seats in the 3rd tiers sell out.
Here is an example of one block. There are about 20 blocks left on sale (mostly in the 3rd tier) so I click on each block, guesstimate the number on sale and keep a running total. Most days I post the figure in the topic.
I'll do it each day so you can keep an eye on it. It's only a guide based on City's online selling system.