One of the things I love about fandom is that you have permission to obsess about tiny details and then run with them and create whole back stories for characters that didn't get explored in canon. I only know Greg when he's appeared in crossovers I've read but I think I've always liked what I've seen of his character in those stories. And I'm so glad that that tiny detail inspired you to write fic - it's one of the reasons we do it, to fill in the blanks :)