Both Sam Waterston and Christine Lahti both played ADAs in the Law and Order franchise. Waterston was on Law & Order (1990) and Lahti was on Law & Order: Special Victims Unit (1999).
At the end, the car collecting Martin Sheen has a registration plate beginning JEB - the initials of his character in 'The West Wing' (Josiah Edward 'Jed' Barlet)
First and only appearance in the series by Christine Lahti playing the sister of Martin Sheen's character.
First of three appearances in the series by Timothy V. Murphy playing Byron, one of Frankie's painting students and occasional hook-up for Grace.
Like the 4 main characters, Christine Lahti also appeared in an Aaron Sorkin show. She played the recurring role of Martha O'del in Studio 60 on the Sunset Strip (2006).