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.

My vague understanding from similar posts on this in the past is not that AA has to reissue the ticket but that they have to in some sense reenter the ticket number into the new booking in order for it to be recognised by other airlines' systems (including BA & CX). It might be worth having another chat with AA and politely asking them if they could reconfirm the ticket number to BA.

AA DO need to reissue the ticket. Not all AA RTW agents know this. Call back AA until you speak to an agent who will reissue the ticket. They should email the new itinerary. I think you get a new ticket number also (even for a date change....crazy....i know)

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