Hey, re your pages for Sesame Street Finding Out Encyclopedia (a great find). Do you have any handy where you can check the contributor credits? Worldcat lists Sue Branch "and others" for illustration (and Carlisle "and others" for writing), suggesting that like The Sesame Street Treasury series and ilk, there were different contributors for different sections.
If you still have access and have time to check, it would help a lot. Thanks!
Also, from that same year, there was apparently also a My Favourite Words Encyclopedia from same publisher and same contributors mostly. From the sound of it (like when The Sesame Street Dictionary was later split into volumes), it might be much (or some) of the same material in one book, if it ever surfaces.
Just a head's up, something weird happened on this one. From the history you can see that the categories were added multiple times. It's probably because the gallery tag wasn't closed. Should be all set now.