There's a flashback that starts at 15:45 on episode 14 of season 1. I've been watching Ranma over the past few days, and I don't think this scene was in a previous episode.
As I recall, the information in the flashback came out as part of a comedy routine. Anime back in those days often had continuity errors like that.
Is this flashback referring to a deleted/modified scene, or is something else going on?