Agreed with D365, 722 has become a christmas tree. It had AC traction fitted but hasn't really had much work since.
With regards spare units, keep in mind how many are stopped on maintenance at any one time and have you also factored in any additional diagrams since the 317/3s joined GA from GN?
I can tell you that there are rarely too many occasions where there are that many service-fit spares. As these things are quite old they need a lot of attention so there are often quite a number stopped.
I hope that helps and isn't just nonsense which only made sense in my head!