https://screenrant.com/big-bang-theory-young-sheldon-missy-failure-bad/

Young Sheldon's version of Missy (Raegan Revord) highlights the fact that The Big Bang Theory completely failed Sheldon's (Iain Armitage) twin sister.

I guess. But that wasn't the show's focus.

Let me get this straight, The Big Bang Theory was supposed to be constructed based on a series that wasn't in existence yet.

By season 4 The Big Bang Theory had 7 regular characters, plus Stuart a semi regular 8th character played brilliantly by Kevin Sussman. How were they going to fit a 9th character in, this was sitcom not a 5 day a week hour long soap opera. One other thing to keep in mind, even if she were just recurring, the actress playing the part is going to come with a premium price tag.

Some other aspects that I think should be pointed out is that there's no reason not to believe that any of the descriptions of the lives of the supporting characters didn't occur either between the timeline of Young Sheldon and after the timeline of The Big Bang Theory.

On "The Big Bang Theory," Missy had two kids, but in "Young Sheldon" Older Sheldon points out that she has had four in her lifetime. Who's to say she didn't have two more after that series ended?

Also, the "knack for entrepreneurship" that the article claimed she had was compromised by a few bugs in her cotton candy machine.

Another factor I noticed is that Mary seems to believe her other two kids are a lot dumber than they really are, just because they're not as smart as Sheldon. It's always possible that they might've picked up on that. Keep in mind, I don't want to turn this into a Mary-bashing thread, because I think she had a tendency to underestimate all her kids. She may dote on Sheldon a lot in "Young Sheldon," but the main reason for doing so is because she's scared. Scared that he's going to grow up to be more of a weirdo than he already is.