Ancestry has Railway Records - including GWR!
There is this entry:
James Smith, born 14th September 1893
Entered service (with GWR) 9th March 1908, Telegraph dept., Cardiff
16th July 1908, Transferred to Clerks dept.
10th January 1908, Passenger dept., Abertillery (Seems to be out of date sync?!)
Previously employed from 14th October 1907
Ill no salary, 16th January 1911 to 19th January 1911
Register folio 2625
Reference to Testimonials: 13306