Is this a current mirror?
Q55 and Q56 are transistors that have multiple collector terminals, where one of the collectors is shorted directly to the base contact.

This keeps the transistor from fully saturating, similar to how a Schottky transistor works in 74S and 74LS type logic. Keeping the transistors out of saturation improves the performance of the circuit.

Not current mirrors. An example of a current mirror is Q60 and Q61.