Was the cream weighed before of after heating and infusing? You may have lost a little in that process, or it may be high fat cream and high fat chocolate.
I think every book recipe needs to be adjusted to your particular ingredients. Cream can be from 30% to 40% fat, and chocolates can have varying ratios of cacao solids to butter in a given percentage. Your 65% dark could be 30% solids and 35% fat or 45% solids and 20% fat or anywhere in between.