Original Commentary

I don't know how Kimberly tells them apart. In the original script, Richard and Sinclair's roles were reversed, even. Maybe the comic takes place in Richard's office - Terrence

Modern Commentary
One of the running jokes, going forward, will be how Kimberly can't tell Richard and Sinclair apart. Well, we'll get there.

They're visually identical. Brisbane and Sandra can tell them apart. Kimberly, Patrick, and Emily can't. I think of it mostly as a test of emotional intelligence. - Terrence