Concorde was always operated with a 100 seat cabin, although there were various position rearrangements of galleys etc over the years.

It certainly is true that at the end it was operated AS IF it was a 2-class aircraft. All those with the cheaper "last flight" tickets were put in the rear cabin. The "real" Concorde pax, who tended to report to the aircraft at the last minute anyway rather than be panting at the gate, were put in the front cabin.