The disc codes were revised once again around 1960.
As to duty numbers, I haven't found anything online, but they were in blocks per shed, which were reorganised from time to time. The individual duties could of course change more frequently.
Possible sources (for random years) are the Express Publishing volumes, the OPC SR Engine Workings volume (Gammell?), the Irwell Press volumes...
If you could be a bit specific (area/years) I have a lot of those and will happily help. You could try joining the semg newsgroup where there are people with first hand info and copies of engine workings (edited: just had a look!).