What a monumental undertaking. From the link article
...By 1935, scholars already had 1 million index cards. It would take more than 30 years before the first of the 21 volumes was published. Most cover a single letter. ...
It’s actually Akkadian (I’m not sure why the dictionary has “Assyrian” in the title), and since it was the lingua franca of the entire Middle East for over 2,000 years, it’s not surprising there’s a lot of documentation.