Question

As Montgomery and de Grey slowly made their way through the message, they noticed more and more oddities. For example, 97556 appeared near the end of the message; the 90000 family indicated important names that were not used very often in messages. We can imagine their shock when they realized that 97556 stood for Zimmermann. That single name fired the men with excitement as they began working on the message from the beginning.

—The Dark Game,
Paul Janeczko

Why were the code breakers excited when they realized that 97556 stood for Zimmermann?

They were proud that they had intercepted a message.
They were excited that the message was full of oddities.
They had never before decoded a name.
They realized they had intercepte

Answer 1

They had never before decoded a name.

Decoding the 90000-series as "Zimmermann" was a major breakthrough: proper names were rare in the cipher, so identifying one gave them a foothold to work back through the rest of the message.