Except that he knew that it was at least 5%. So you'd actually have to figure out how much the discount already included in the value is for that 5% (which is highly subjective, but the discount is almost certainly not also 5%), and then multiply it by six-fifths (maybe, because the discount is also almost certainly not linear).

Of course, this is all a moot point, because what an actual businessman (as opposed to a con artist) would do, if they were concerned the bot stats might be inaccurate, is make sure the agreement had specific terms in it as to what would happen if it was found to be inaccurate.