TV appearances by the Muppets, where show titles and dates are unknown. When information surfaces, these items will be moved to their own pages.
Pau Hana Years
Big Bird and Oscar appear in the 1000th episode of this show in 1977. This was probably filmed during the Sesame Street cast's visit to Hawaii.
A video filmed by one of the show's producers documenting the production of the episode can be found here:
Some footage of an appearance by Jim Henson and Kermit on an NBC show was included in the Kevin Clash appearance on The Big Idea.
Promotional Disney Appearance
The red book has info on a guest appearance in a Japanese show/special, but it doesn't reveal the title.
1983 Kennedy Center Tribute
Someone on Muppet Central Forums found this video, but doesn't appear to have a page.