Sorry, but I remain unconvinced, and we may have to agree to differ.
G-BOAC was started first, had the earlier production number, #204, and first flew on 27 Feb 1975.
G-BOAA was started second, had a later production number, #206, and first flew on 05 Nov 1975, nearly nine months later than G-BOAC.
As for quoting the structural completion
dates, with respect, even if they are accurate, I think they are fairly meaningless, as traditionally the maiden flight date is used as an aircraft's birthdate!
The reason I suggest that the structural completion dates may not be accurate is that the dates you quote are actually the registration dates of the aircraft concerned. Not the same thing, and I would doubt that the aircraft were registered on exactly the same day they were completed.
If you obtained your figures from http://www.concordesst.com
, Gordon Roxburgh's excellent website about Concorde, I wonder if you missed the following comment regarding the fleet ages?
If I may quote: ...As G-BOAC is the oldest Concorde in the BA fleet...
What's the expression in the USA? Close, but no cigar!
Seriously though, it's great to see such interest in Concorde coming from fans in the USA. Long may it continue.