Nothing at all would happen apart from the fact you'd be angry to know you had paid more than you should. In fact, this is a very very usual situation - booking systems for all airlines review the allocation of the seats in each fare class every night by 'correcting' their prediction for actual bookings etc. So for instance, if you want to fly Easter Friday and the computer finds that now, 6 months before hand, 20 seats have been sold in the plane, the computer will decide that they can sell all else as B and you might not find anything in any other class. Similarly, if in early March, only 50 seats have been sold, the computer might then ring the alarm and release some seats in V or N. Of course, if you booked in B, you could always cancel the tickets, get your money back and buy again, but if you booked, say, in T or L you'll just be screwed. Again, this is just normal with all airlines, they all say that it is 'usually' to your advantage to book early but they know perfectly well it is not 'always' to your advantage to do so.