Re-using the bogie underframes from “pairs” carriage F.50 (which consisted of two 1873-built four-wheel passenger carriages B.7 and B.8) these two carriage bodies were removed at St. John’s Station in the spring of 1968 and discarded in the yard, later being scrapped on site.  The underframes became the final of this then-unofficial series, R.12...

...some sources state there was a thirteenth such runner for which there is no supporting evidence. This was notable in only carrying its fleet number in chalk.  The frames were later changed back to their original fleet number F.50 and in this form it remains today.  It carries both F.50 and F.64 lettering further compounding the riddle of this series!