Nikon Scan 3: shadow detail query

Hi Folks,
I'm in the processing of scanning a lot of old black and white
negatives using a Nikon Coolscan 4 and Nikon Scan 3.1 software. The
files are then brought into Photoshop 7 for post processing. I've
begun to notice that all the images sem 'underexposed', when viewed
using the histogram dispay in the Curves Tab in Nikonscan. Photoshop
also confirms this lack of shadow values on scanning. It seems that
every images requires its black point to be adjusted in Photoshop.
I seem to remember a previous thread mentioning the fact that
Nikonscan had a 'faulty' histogram display?
I'd appreciate any help or advice. Incidenatlly, the negatives are not
underexposed!

Thanks in advance
Stephen