Revealing mistake: When Charlotte is putting her diamond ring on in her apartment, there is a close-up shot of it. It is a large, circular diamond on a simple golden band. This is not the same diamond engagement ring she has been wearing previously in the series. That ring had two parallel silver bands, and the diamond looked slightly different.
Revealing mistake: When Samantha is surprised at Richard's apartment by his assistant, she quickly throws her towel around herself to cover up. But the towel rides up too far, and you can see that Kim Cattrall is wearing tan or nude colored underwear. Soon after that, Samantha makes a comment to the assistant that implies she was nude under the towel. So the panties were probably for the benefit of the actress, to protect her modesty below the waist.