They were replaced with kinescopes that had been sent off to other time zone and countries that didn’t have the ability to record a program over the air and then show it at a later time. They stopped doing this for the later episodes after technology caught up in places like Alaska. I remember reading an article about it, but can’t remember when or where.

All three of the DS What's My Line appearances are available for viewing on YouTube. The three clips have been posted together as a Dark Shadows special program which means that it's probably been directly from the DVD.