I mean, I agree with you. I was just saying I found a different, more clear source back on January 4th. Which thankfully Flip just reposted.
The links you keep giving contradict themselves, because that same guidance (150 Day Assessment guidance) also says very specifically:
So Gov.UK contradicts the hell out of itself.
But the Common Issues: Validation link is very clear in what it states, which is that the clock starts upon receipt of the application, not validation.