The histogram on the right-hand side of the Unsub dashboard has three sections: those titles with cost per use (CPU) equal to or less than $100, over $100 CPU, and no paywalled usage (and therefore no CPU value).
Sometimes titles in the "no paywalled usage" section at the bottom of your Unsub dashboard can have greater than zero uses as shown in the example below.
The downloads seen in the image above come from the COUNTER report you upload. We then calculate paywalled uses by subtracting out uses you get for free either through open access or post-termination access. You can then end up with paywalled uses less than 1 or even 0 or a negative value.
Whether the real value for uses in a case like this is 0 or 0.5 or 1 we think does not matter. The titles in this category have essentially no usage.