It’s also possible that they can’t track new installs either.
FAQ:
How is Unity collecting the number of installs?
We leverage our own proprietary data model and will provide estimates of the number of times the runtime is distributed for a given project – this estimate will cover an invoice for all platforms.
Which is some kind of weird nebulous BS.
They’re not saying their engine phones home and/or collects data from end-user devices. With the associated data protection nightmares.
Control over individual updates was abandonded halfway through Windows 7, when they found out their algorithm for evaluating updates is exponential and has trouble finishing within 24 hours. So they moved to a linear sequence of all-or-nothing bundles and diffs.
They used to offer two tracks of those: everything and security-only. I don’t think they do that anymore either.
You can uninstall individual updates after the fact. Not sure this actually works to any useful degree.
Unity themselves have committed to that option (if you don’t like our new future TOS, keep the old version and don’t update) in writing (that was in their deleted github repo). So it seems extremely likely that they would lose in court.
The key words in the above are ‘in court’. If you’re an indie unhappy with an x*$.20 charge, chances are a lawsuit will not improve your day.