Am currently mid-way through an AA issued DONE5. Have changed
various dates (not routing) along the way with no problems. Needed
to change dates today on some CX and BA sectors so did this by
phone with AA with no problems. New BA flight date for MEXLHR
showed straight away on ba.com but even with status it won't
allow me to prebook a seat.

I called BA in Australia (where I currently am) who said ba.com
would not allow me to pre-seat until AA had re-issued the ticket
to reflect the new date and that they couldn't even pre-book a
seat in the CRS until this was done. Called AA back who said no
re-issue was needed and what were BA talking about.....
Having previously changed a JL sector with jal.com allowing me
to go in a pre-book a seat straight away I tend to think AA are
right....

Anybody had the same scenario? Any advice please. My fave
62A/K are available on the BA flight and I'd rather like one of
them.