Ah, just found the route on the Newquay info - but still confused by the dates considering the route is axed 2 months beforehand.
The advert will most likely have been made and displayed to be published before the announcement of the closure of the MAN base happended despite the date ranges. Im guessing it's a minimum (''from...'') price offer displayed most likely, which will have meant the need for the date range to be shown. It doesn't neccessarily mean however that the route would/will have run throughout the period stated. Hope that helps.
On another note though, I must say, the advert clearly did the job it's designed to as you now know of the bmibaby Newquay routes?