profiling scanner

Hi

I've just bought a scanner and have profiled it with Vuescan, the results look good but I have a question about the IT8 target. Basically, the profiling marquee produced by Vuescan doesn't cover the entire target (I'm using a Silverfast target which differs from say Kodak's, which have a photograph of a woman’s face on the right hand side where the Silverfast has three extra columns). The Vuescan marquee fits perfectly around the target area excluding these three columns, does anyone know what these extra columns are for and if it will make a great deal of difference to the profile produced? Vuescan does offer advice on where to purchased targets and one of their recommendations has the same format as the target I'm using.

Thanks

Jon