User blog comment:Argorrath/Treyarch posts a message of zombies; possibly hinting to a DLC 4/@comment-76.228.209.177-20130801003259

The letters sound like they might possibly be from the original crew, before the main Nazi Zombie events, but then again the 1917 date is completely throwing me off. Either there's gonna be more time travel, or it's simply backstory.

Or both.

Oooh, a Zombie's map that tells of the true origin behind it all? Before Die Riese? Maybe the origin of Group 935?

Only 'time-travel will tell'! HA, get it? Cause it's a reference to the achievement, and to the phrase 'Time will tell' cause we gotta wait till we find out. Yea, I'm funny...

...no I'm not...