Usual promotional progression on the railway would be as follows: 1) Starting grade Porter, or labourer etc. 2) Shunter 3) Freight Guard 4) If available Passenger Guard. Further promotion wopuld be into a salaried grade job as Station or Yard Inspector, and then possibly Station Master.
A person could and sometimes was demoted as part of a discipline process, so it is possible a person could be in a higher graded job in 1901 than in 1904. What is not usually possible is for a man to move from this line of promotion to a footplate job, and certainly impossible in this era if he was over 25.