I'm pretty sure it is not as clean-cut as SRG suggests. Some pax are more commercially important to BA than others, hence why BA assigns a commercial importance value to its pax (no great secret there).

In the past, I've had to buy a full fare one-way Y en-route to the airport with the Gold line. Therefore arriving at T-1h, I'm probably going to be one of the last to check in. Given that I'm a Gold, my CIV would be at least 38, I'd just bought a full Y, if that flight were oversold, would I be offloaded in favour of a O bucket CIV0, just because I checked in late? I would err on the side of unlikely.