Let's just say no one's ever been able to make head or tails out of the numbers on Colnagos until later in that decade, and plenty of people have tried. The number on the BB of yours could have been placed there by a subcontractor. I would bet your Colnago is from the same period as the one in that bulgier catalog. I also owned one from that same period myself (maybe it didn't have the derailleur braze-on, I can't recall). Sometimes the presence or absence of chrome is meaningful on Colnagos, other times not. Colnago was selling a lot of bikes at that time, and some don't fit the mold. Mine had a chrome fork.