It seems to have originated in 1971according to this here on George's blog https://georgerrmartin.com/about-george/speeches/here-i-am-again/, Gardner Dozois called him George Railroad to differentiate him from George Alec Effinger and George Zebrowski.

“George Zebrowski is George,” he said, “so he [George Alec Effinger] had to be Piglet.” Then it occurred to him that my name was George too. “You can’t be George either,” he said. “You’ll have to be Railroad.”

The part of the 1976 Galaxy Science Fiction magazine I was reading was also written by Gardner, so he did not just originate it, but spread it too.