Oh yes, had that one last year

Client: why didn't you calculate my child tax credit?!

Me: You have children to report?

Client: Of course I do. It's in the organizer.

Me: I only see that you mention one was born a couple months ago in February ...

Client: Well what do you think I am talking about?

Me: (sigh). We are filing a 2021 tax return. The child was born in 2022.

Client: Yeah, but I haven't filed the return yet. I want to claim him.

Gotcha.