Hi I'm Jan Van Quirm and I'm a Jilly Cooper-a-holic
Jilly's nothing to do with Terry of course but when I first cultivated my shameless 'habit' I tore through her early and not quite so horsy books and found that one of them, Octavia, I'd read before when I was about 13. It drove me mad trying to work out there the hell I'd read it before the publication details (I knew I'd not read the book at all before). Then finally I remembered that Ms. Cooper used to write serial fiction for teen mags and I'd read a truncated version of it in Petticoat
severalm years before (this is going way back!
Maybe Terry did something similar and did a short story or serialisation version of CoM before he got famous?