A knowledge cutoff is the date after which a model's training data ends — without retrieval, the model's picture of a market is frozen at that date.
A model trained through last year does not know this year's product launches, rebrands, or shutdowns — unless it retrieves. That is why the same model gives different recommendations with browsing on versus off, and why new brands break into grounded rankings long before ungrounded ones.
For challenger brands the cutoff is the moat to cross: the incumbent is in the training data; you have to arrive through the sources the model reads at answer time.