I just got a bump voucher from NW for $300. With the situation as it is, it's not unreasonable to hope I might pick up another one or two as time goes on.

I was hoping to use them for an international ticket, but I'm told that you can't use more than one per ticket. Does any airline allow you to combine vouchers?

I'm not sure of the reasoning behind this. If they owe you the money, what difference does it make whether you spread it out over several tickets or use it all at once?