Sensitivity

What am I reading wrongly here - on the Sony product pages, under the line "Sensitivity (2000 lx, 89.9% reflectance)" the SRW9000PL has T11 and the F5 has T13 - I make that about half a stop, but I thought the base ISO was meant to be 500 and 2000 respectively?
Steve
 
Ive never understood why video camera white papers show sensitivity this way, if anyone knows please enlighten! I also notice they usually only give these numbers for interlace mode.
 
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