What Bamforth is saying, if you read that section of Chapter 6, is that before and during fermentation, so long as they are not bound up in other compounds and therefore not “free to roam”, active yeast will consume those carbonyl substances. If they are already roaming free and oxidized in a finished beer, the deal is done.
No amount of virile yeast at that point can reverse oxidative damage.
EDIT: What’s strange is how strong a statement this is
“I think the answer lies with yeast. Yeast loves to reduce carbonyl substances. If you take a beer with pronounced cardboard/wet paper character and treat it with a good virile yeast, the stale notes will be removed.”
and how it seems to be contradicted in the very next few paragraphs by Bamforth.