Because the Railway was an 'Entity unto itself' and didnt have to seek approval when doing lots of things on Railway land, things came and went without it being recorded elsewhere.
I can remember the Lithgow District Superintendent and the ADS came to Katoomba one day and inspected all the notices, both Public and Departmental that adorned the Station and Subway so I gathered advertising was of some importance to them.
No doubt records would have been kept back in the Office (Pie Shop) at Lithgow until the last Clerk was made redundant and in came the 'Skip Bin' and took it allll away........
Mudgee, being in the ESK (Lithgow) District, their records would have been kept in Lithgow, I doubt much would have been transferred to Orange when it took over the district but after that..........
The only other place I can think of where records might have been placed was into the Real Estate section that was created to handle the use and sale of railway Land and property.