Since most (or all) mysteries require waiting until the end of the mythos phase to officially complete them, is there no point to continuing the game once you flip the final mythos card and still haven't solved the first 3 mysteries? The exception to giving up the moment the final mythos is flipped seems to be when the ancient one awakens and you stand a chance to defeat him in that final round after the last mythos is flipped (since defeating the ancient one appears to end the game immediately in the investigators' favor). 

Do I have this all correct?