The official way to define a sprint goal...

... doesn’t exist of course.

But please:

“We'll do stories 5712, 3211, 7621 and 3123” has never been a sensible commitment. That’s not why we have sprint goals.

The Scrum Guide states “The Sprint Goal gives the Development Team some flexibility [...]” and “The Sprint Goal can be any other coherence that causes the Development Team to work together rather than on separate initiatives.”

So, if you ask me

“At the end of this iteration department Y will be able to sell product X via channel C” sounds much more like a useful sprint goal. And much more in alignment with the original ideas of Scrum.

IMHO, one of the most important things about the sprint goal is that little word ‘coherence’ - a clear sprint goal helps in setting priorities, aligning team efforts, and communicating with stakeholders.

Therefore, I suggest to use more than a collection of stories to define the sprint goal.

till next time
  Michael Mahlberg

P.S.: Using numbers to drive a business is considered harmful by many people – to quote W. Edwards Deming Quotes

People with targets and jobs dependent upon meeting them will probably meet the targets - even if they have to destroy the enterprise to do it.

Perhaps sprint goals made up of (story) numbers are also a bad idea.