Oops!

[rustyrider]

But could they give Nick the benefit of the doubt that his speedo may have been reading up to 10% less than what his actual speed was though?

It doesn't work like that.  To meet type approval a speedo may over read by up to 10% but cannot under read by any amount.  So what your speedo shows will always be up to 10% faster than you are really travelling at, never less.  So to be doing an actual 91 mph, I suspect the speedo would have been reading nearer the ton.