Was 1974 indeed the first year the Sesame float appeared in the Macy's parade? This video seems to imply that it was around as early as '72. Of course, the uploader easily could have gotten the year wrong.
I've also mentioned in the article that despite what is mentioned in Sandy Duncan's introduction to the cast during the '88 parade, Susan does not appear to be in attendance. That could be Uncle Wally sitting on the front right (our left) of the car, but I'm not at all comfortable with that.
According to the timeline published in Sesame Street: A Celebration - 40 Years of Life on the Street (which, granted, is not without its errata), the 123 brownstone first appeared in the parade in 1974. Also, if that's the cast of The Wiz at 0:50, that show didn't open until 1974 and wasn't on Broadway until the following year. So, I'm guessing the YouTuber got the date wrong.
As for the 88 parade, I don't see Loretta Long either — even though no one gets a close-up and all their faces are distorted from the age of the video and compression issues — I definitely hear her on the pre-recorded track. I'm not sure how best to deal with the wording on the article in that case since, again, it's hard to confirm who's sitting on the float.