I have stumbled across a handful of cases where a movie record lists cast members for which the corresponding person record is missing. For example, in Back To The Future (TMDB ID 105) there are five cast members listed with person IDs but for which no records can be found.

• Ethel Sway (ID 2749695), who plays Wilbur's wife
• Randy Feelgood (ID 2749694) as Zoot Boogallo
• Kiki Ebsen (ID 2749693) playing a band member
• Richard Patrick (ID 2333453) playing a teenager
• Janine King (ID 1200797) plays a student

I would have expected standard database referential integrity to have prevented this from happening, but it appears my assumption was wrong. I've come across four other movies with cast members whose person records have disappeared (in some cases, a repeat of an actor appearing in the first list).

• Zay Domo Artist (ID 4712763), playing Milo in Kingdom of the Planet of the Apes (ID 653346)
• Janine King (ID 1200797), an uncredited literary fan in Ruby Sparks (ID 103332)
• Richard Patrick (ID 2333453), who plays a beachgoer in The Karate Kid (ID 1885)
• Li Dan (ID 3329911) in the rôle of Xiao Laizi in Farewell My Concubine (ID 10997)

One side note: I'm not 100% confident the formatting on this message will survive intact, as the lists don't show up as lists when I hit the Preview button.