To expand on another answer here -- there are more values in the PRF than there are names because "old" instructions in flight can refer to outdated versions of

To expand on another answer here -- there are more values in the PRF than there are names because "old" instructions in flight can refer to outdated versions of architectural registers (the names). But a new instruction can only see the latest versions of the architectural registers, so only those 16 actually matter w.r.t. future execution: when we switch back to the task, its new instructions will ony need the 16 live values.