With millions of unsold copies of it's book, "I Am Not Spock's Brain"
If there is a copy of Discovery, it could have happened in the wormhole, when the ship encountered the gravitational hibbedy-jibbety that caused it to be a year late. The ship we've been seeing came out a year after Burnham and the copy didn't travel forward in time at all, but stayed in the nebula for 1000 years.
I can get on board with this explanation. What happened to the crew?