There are 6 episodes considered lost

520503 002 Ben Thompson (Act 1 had been discovered)
520517 004 Dodge City Killer
520614 008 Jailbait Janet
520621 009 Heat Spell
520626 010 The Ride Back
600619 428 Homely Girl

There are 3 episodes for which only rehearsals exist

520927 023 The Railroad
530808 068 Sky
530815 069 Moon