Then again, maybe it was a flub on Joel Crothers' part - he said "Molly" instead of the scripted "Amy" in reference to Chris' kid sister - and the scene wasn't re-done, producers assuming "this episode will never be seen again anyway..."
Molly was indeed the original name for Amy. Chris is also named "Bob" in these summaries.
but Amy isn't the only example of a character being renamed after having already been referred to on the show as something else. For example, 1897's Edward was originally named Oscar, and in Ep #643 Roger discovers a letter Quentin had written to Jamison about Oscar.
Do we have documentary evidence for the Julia(n) "typo"? Bob Costello and Grayson Hall told conflicting versions of how Grayson was cast on the show. In Grayson's version, she got a phone call, got dressed, and cabbed over to the studio for her very first episode, which was recorded the very next day. Talk about instant casting.