Reply To: Book outbound add return at a later date

[NorthernLass]

Yes to the open jaw and you would have to call, at least to add the inbound leg.
It’s not clear whether BA would agree to book the inbound many months after you’d booked the outbound, but I think theoretically it would be possible if you pointed out that there was no availability previously.
As I understand it, you can’t make any changes to a 241 itinerary less than 24 hours before departure of the outbound, so I’m guessing this might also apply to the upgrade voucher.