What must be remembered is that not all CA members are British or they are but reside on foreign soil. I think this has been catered for in the shirt design by your choice of having the Union flag on the sleeve.
Also, whilst the Aston is very a British car, they are not so parochial (nationalistic??) as some teams as they do not insist on an all-British driver line-up. The design of the shirt, as it stands at the moment, is to reflect the anniversary of the
Team's success 50 yrs ago (driven by a Brit and an American) and it's continuing involvement in the race.
Who knows, next year we may opt for a pic of the mighty 917 to mark the 30th anniversary of Porsche's first victory (driven by a Brit and a German)

Del