I may be teaching grannies to suck eggs here, but in all the years (decades) that I have been using Derby station, I hadn't realised that Northern run a "regular" service from Derby, I thought that EMT and XC were the only operators. But arriving at Derby station late-ish last night, I spotted a 2239 Sheffield train on the board advertised as a Northern service. "Some mistake" I thought, but no it was correct. As far as I can see, it doesn't appear in any of Northern's pocket timetables, so presumably they are not too keen on people knowing about it! Well, the train appears (the 2215SX/2217SO from Nottingham), but no mention of any Derby stop. According to Wikipedia, there is a return service early morning that does not stop at Derby, but I cannot find anything that matches in the timetable. However, the Northern service 2003 from Leeds does stop at Derby - again this stop does not appear in Northern's pocket timetable. Arriving Nottingham 2202, I presume it then forms the 2215SX/2217SO departure back via Derby. Why do Northern need to maintain route knowledge via Derby? Surely, if the route Sheffield to Nottingham via Alfreton is blocked, both XC and EMT run plenty of services Sheffield to Derby and then to Nottingham.