Originally Posted by
LTN Phobia
I have already given it a try on JAL (revenue) and BA (miles) and 31 March (or 25 March) definitely does not work. You can see availability on BA.com but cannot book, and JAL returns an error.
Don't know why it doesn't work for you but I can 100% book (or at least take the booking all the way to the payment page) HND-CTS on 31st March.