Originally Posted by
irishguy28
The price charged to a "new" customer must not always be the same as the price offered to an existing customer seeking to change an existing ticket.
There is never just one price for a flight, so checking what a customer would be charged today on a hypothetical booking is not a reliable guide for what fare difference may be applicable in your situation.
This is true for all airlines and is not AF/KL specific.
One of the reasons for this is that the website, when selling a new ticket, might apply some dynamic fare discounts. But during changes, or manual calculations, the published fares would be used. It is not the only reason, but one of them. Of course, there are situations where a published fare that you are booking into ends up cheaper than what you originally paid, and in those cases, AFKL usually provides a voucher for the difference.