You sure it's that one? My source suggests there is no 245 or 246. Also, they are N24x LHTSteppy dart 46246 (N246 LHY I think) is still knocking around surprisingly, saw it working the Bath to Devizes 271 the other day, would have loved to have been on that!
Anyhow, I saw two consecutive step entrance Darts on the 231 last week. I wouldn't have liked to be on either of those.