http://www.youtube.com/watch?v=m3-wG6z1uB0
Looks like he had already established his natural stride length for elite times back in 2004.
I counted approximately 81.4 knee raises from blocks to line or 80.4 if you counting true strides. In 2006 when he was trailing gay, carter, and spearmon to sub 20 clockings, i had wondered about how many strides he may have covered the 2004 19.93 run in. I figured it was something like 82 or 83 strides.
Longest strides ever seen bolt run with was lausanne 2006 when he ran 19.88 behind carter and gay. He covered it in approximately 80.4 knee raises from blocks to line or 79.4 true strides.