Well, several of the Windows 7 updates in the past year have been known to be... questionable. It's like a rat's nest at times. Many have re-installed things like telemetry, so you have to figure out which updates do what. I tend to be a month behind on patches for that exact reason: I err on the side of caution. It's saved me a LOT of pain, let me assure you.
Windows Update taking like 9 billion years to "figure out" what all the updates are that should be available to you is actually solved through several "sub-updates". So if you haven't gone through the pain of doing that (installing specific KBs that fix it), that's probably why. If your "Windows Update" scan previously took, say, 15 minutes, these KBs/sub-updates can actually bring that down into the under-a-minute range.
Let me know if you want details. I actually slipstream all of this stuff into my own Windows 7 ISOs so that I don't have to deal with it again. I think I have a list of the KBs and what not in my
slipstream.bat.
A great website to start following for stuff like this is
https://www.askwoody.com or follow him on Twitter at @woodyleonhard -- he works for ComputerWorld.
And let's not forget
with things like Meltdown/Spectre, figuring out used CPU time is way more complicated than it used to be. Worth watching if you care about low-level details, trust me. (And yes, these apply to Windows too)