507001 is on the New Brighton line, working .35 departures from Liverpool Central. Another booked move to Kirkdale didn't happen last night, but surely it will be on the Southport line before long.
Not sure 507003 has returned to service from overhaul yet.
Christmas shopping and football matches may well change this, but I think it's currently 18 on a normal Saturday (10 Southport line, 4 New Brighton and 4 West Kirby). I imagine the next couple of Saturdays will see at least some six-car operation on the Southport line as there were reports of passengers unable to board last Saturday.