I thought I had bought Anna and Elsa but it wasn't in my orders. If someone else bought it,
you can look in your orders and choose "save as" on the picture and it shows the pin #.
So, you just inspired me to look through my past orders. I do not remember ordering this Anna/Elsa but I guess I did (I might have ordered it for someone else and don't remember). I did this trick and it tried to save as pin 78. So that mystery is solved.
ETA: I also uncovered some intrigue! I went into my orders, then instead of trying to save the image file copied the web address of the photo and pasted it.
https://s3-us-west-2.amazonaws.com/.../static/Catalog/DVDproducts/271x384/PIN77.png (this is for the Sleeping Beauty frame pin)
I changed the PIN number to a few of the most recent and each time I did it downloaded an image file, which upon opening was the correct image for those recent pins. I then tried it with the range you are looking for. 76, 77, and 78 downloaded, but then I got an error for pins 79, 80, and 81 and then back again for pins 82 though 87 (the current most recent release, panda Mei).
This is the error code given for pin 81. (I screencapped it and posted it as a photo in case pasting the actual code did something wonky). The code for pins 79 and 80 looks the same except for different text in the RequestID and HostID fields.
Changing the image code for pin 75 went directly to a screencap of this Ursula pin: