By the way.....if you want to know more about airframes etc see:
<a href="http://www.bird.ch/bharms/asr_sh00.htm" target="_blank">Aircraft census</a>
..and click the concorde link.
You will see that out of 20 airframes, a few are pre-prod models etc (which I guess had minimal/no supersonic hours??)
I guess that is why the stats are based on 16 a/c.