It's not uncommon to see other depot's 156s/142s (more so the latter) on other runs around different regions. All to do with replacing units or having different maintenance regimes.
If Heaton want a 156 to Allerton (for overhaul for example) it's put onto various diagrams to get it down there. For instance ending up at Carlisle one day, then Barrow, then Newton Heath then Allerton.
RE: Northern Rail
![[Image: 0a85ed5b4e97324e338555472f222830.png]](https://public.railmiles.me/signatures/0a85ed5b4e97324e338555472f222830.png)