But it was quite amusing to see in my own eyes: computer mostly worked fine but occasionally would cry what "Can't load library at C:\WINDOWS\system33\somecorewindowslibrary.dll".

I didn't even notice at first just though it was a virus or a consequences of a virus infection until I caught that '33' thing. Gone to check and there were system32, system33, system34...

So when the computer booted up cold at the morning everything were fine but at some time and temp the unstable cell in the RAM module started to fluctuate and mutate the original value of a several bits. And looks like it was in a quite low address that's why it often and repeatedly was used by the system for the same purpose: or the storage of SystemDirectory for GetSystemDirectory or the filesystem MFT.

But again, it's the only time where I had a factual confirmation of a memory cell failure and only because it happened at the right (or not so, in the eyes of the user of that machine) place. How many times all these errors just silently go unnoticed, cause some bit rot or just doesn't affect anything of value (your computer just froze, restarted or you restarted it yourself because it started to behave erratically) is literally unknown - because that's is not a ECC memory.