I mean, theatre generally doesn’t deal with the concept of “canon” in the same way other media forms do, but even if it did, I guess the answer would have to be no, since it wasn’t affiliated with the creators of the show. Or at least I doubt it is
Sheldon Harnick mentored the author and has approved its content, though he did not write any of it. It’s a fun read- almost like late period Tarantino meets Fiddler.