I have a confirmed booking for an upcoming BA trip to the US. EDI -> LHR -> EWR / EWR -> LHR -> EDI. It shows as expected in Manage My Bookiing and I have been able to choose (and pay for) seats for 3 of the legs. For the final leg. the site shows no seats available! Note that whole trip is Club Europe / Club World. Does this mean the flight is over sold and I can expect to be downgarded or denied boarding, or is this normal and seats will open up closer to flight departure (several weeks away).

Thanks for any info.