I suggest you look at Apple's documentation as this was introduced in macOS 10.2 long before 10.8.1:
https://developer.apple.com/document...urlerrordomain
It's just an error condition that describes a particular problem, but you are suggesting it's some kind of inherent bug, but it's not, it's a descriptive message when something goes wrong. It doesn't mean the problem is macOS. The problem was Virgin Media.
Please do ask your engineer to provide a detailed breakdown that explains why a generic error message that can have multiple explanations, incuding issues on the wider Internet, could possibly be an issue only related to a problem with macOS itself, yet somehow only affected macOS users on Virgin Media for a 36 hour time period, and how if it is a probme with macOS itself an affected machine was not experiencing the issue connected to EE yet was experiencing the issue on Virgin Media, and how any of this is to do with network preferences (note the documentation doesn't mention network preferences at all) when it was affecting me with a brand new Mac trying to do its first update and install Rosetta 2, and another customer I found who was trying to perform Internet Recovery to reinstall macOS on their machine. Neither of these machines had any network preferences that were not default.
Also it would be nice to understand how a network preference issue affected all our remote workers on Virgin Media at the exact same time, and none of our office workers on AAISP, and how it stopped affecting Virgin Media users at the exact same time despite nobody changing any network settings.
If you bothered to read anything I wrote you'd know I looked quite deeply in to this and the error in this case did seem to relate to an inability to create a TLS connection with Apple's updates servers. Again, we know Apple's certificate was valid as it worked for other ISPs. We also know Virgin Media have the technology active on their network that can break TLS connections, just go to the https version of any piracy site that's blocked and if you have a decent browser it will just show an SSL error because it rightfully refuses to load Virgin's modified content. We know this issue only affected Virgin Media users. So what's your logic for concluding this was not a VM issue?
Also I did look on the Apple forums, and as I said above, this error message can have multiple explanations, but almost always some kind of TLS issue. The most common issue I found was that the system clock was wrong, and an accurate time is needed for establishing a TLS connection. All of the Macs concerned had an accurate time set.
I'm an engineer too. I'm not stupid. I spent hours going through every possible cause. The most likely explanation is: Virgin Media. And it doesn't seem to be a coincidence that a few hours after support agreed to escalate my issue to their network team that it was fixed.
In summary, I don't think this was a bug in macOS. I think this was macOS doing its job and refusing to connect to an untrusted source.