This information is not stored in Service/Maintenance Contract. It is stored in Included Services, which is a child object of Service/Maintenance Contract.
The details stored are Allowed Units and Consumed Units, which are the fields available out of the box. Remaining Units (no field available out of the box) need to be calculated as (Allowed Units - Consumed Units).
I noticed that if you do not have an allowed unit defined the auto-entitlement will not grab the included service, however if you go to the check-entitlement screen the included service has an available quantity of unlimited. What is the recommended path to get this setup properly so we do not have a specified quantity of allowed units but can still get the 'Included Service' referenced properly? Without the Entitlement History record referencing the Included Service record 'Get Price' will not pull in the appropriate data.
As interactive entitlement provides the option to the user to choose the appropriate included service, it lists the included services which do not have allowed units also.
Auto-entitlement, where user does not get to choose, applies more restrictive criteria.
To ensure that an included service is considered by auto-entitlement, you can set it to a high enough number so that it is considered as a valid service for the duration of the contract. Alternatively, you can define a workflow rule with field update, to automatically set allowed units to a valid number, whenever it is null or 0.