My understanding is that vacancy means available units for rent. So, plausibly, if you say 50 of the 100 units in your building aren't available for rent because you say they're being painted then they don't contribute to the vacancy of your building.

That's almost the exact opposite of your definition, but I agree that a 1.4% vacancy rate means there's almost nothing available for rent.

I'm having trouble finding an official definition from a source that reports them, but my definition matches things that I can find online, eg https://www.brickunderground.com/rent/vacancy-rate-what-does...