Every team member can carry a cost rate alongside their charge-out rate — what an hour of their time actually costs the practice. Time is valued at the cost rate that applied on the day it was logged, so a pay rise this month does not quietly rewrite what last year's work cost.
Cost is recorded whether or not the time was billable, because unbillable hours cost exactly as much as billable ones. That is the entire point: a client who absorbs six hours of unbilled queries costs you the same as one who absorbs six billable hours and pays for them.