As per the current implementation of entitlement report Quantity shown here https://github.com/theforeman/community-templates/blob/7c2ee7a486a534ca54e4f37173778f5134ff3cc5/report_templates/entitlements.erb#L28 is the total quantity of that specific subscription from the Pool.

It is required to show the quantity consumed not the over-all quantity of the Subscription pool.