Could be related to a change I saw recently, the likes of LGW-BCN was wide open all year for £80-90 J each with 4 seats left on most flights far in advance. Dropped to only 1 seat a couple of days ago, making a planned little jaunt of mines for two disappear for all the dates. While the sale might last till 30th January, the seats seem to go through amount changes at points during the sale. I guess the rule is always book and cancel in 24 hours if needs be...