Like @flatcircle the current offer I received (the ONLY one I've gotten this year) included one I already have booked. I called in to compare prices and it was much lower, but required payment in full at time of booking.
So, being booked doesn't seem to prevent one from getting an offer and seeing one you're paying "real" money for essentially being given away stings. Reading about offers on "your" cruise is one thing, having one sent directly to you is quite another. I really do want HAL to be health and if offering huge discounts on certain sailings helps them achieve that, I'm ok with (well, actually I'm not, but I can get there), but they should update the algorithms to remove current bookings before sending them out.