In that you noticed that it seemed to be an inconsistency, and that he's claiming here to have put that inconsistency in intentionally.
As for the other stuff, oh totally, he's come up with new stuff and changed stuff. Actually, the character of Butters is one great example of that: Butters was originally just supposed to be a one-off character in Death Masks. However, Butcher ended up liking him, and brought him back for Dead Beat, and he grew from there.