Well, hold on a second. There definitely seems to be some conflicting information in here.

Normally, a Gold companion will be upgraded AFTER all Platinum Elites, Platinum companions and Gold elites.

The question here is whether the fact that the Gold companion is on a B fare "bumps" his priority up to the Y/B "section" at the top of the priority list, or whether the Gold companion is still processed behind ALL Gold elites, just receiving the benefit of the B fare among other Gold companions.

I have not seen any information to suggest that a Gold companion on a B fare gets treated with the higher priority, ahead of Platinum elites on sub-M fares. Co.com is not particularly specific about the ordering of companion upgrades. I would be surprised (but not shocked) if they would upgrade a Gold companion on a B fare ahead of a Platinum on an H fare.

Non-elites on full Y fares are entitled to upgrades (they stopped publishing this benefit as it happened so rarely), but those theoretically get processed after ALL elites, not after just Y/B elites. I suspect it's the same with companions.