In 1x11, Blood Calls To Blood, (scene starts at 20:08) when Luke and Clary are headed to Renwick's to find Jocelyn and Valentine, they talk about "Michael Wayland" who is suddenly alive again. Clary is suspicious about him, and at some point in the conversation she asks "Was that 19 years ago?", and Luke answers "20. Why?", and then Clary responds with "20..." as if something doesn't add up there.
I don't understand this conversation at all, firstly because they are talking about two different time periods as if they're referring to the same. Firstly the time period of the Uprising, when Luke turned into a werewolf and when Jocelyn ran away while pregnant with Clary. Secondly they talk about when they believed Michael Wayland died and the Lightwoods took in Jace, but at this time, Jace was around 10 years old (I don't remember exactly how old). Following this, Clary asks if that was 19 years ago. However, we as the viewers have no indication of what happened 19 or 20 years ago exactly and we don't know anyone's age besides Clary, so there is no way to know what Clary is thinking and why this doesn't add up.
So is it just me or does this conversation not make sense at all? I would love it if anyone has an explanation, because I'm rewatching the show and this has bothered me every time I watched this scene.