It just means it's not the only premise available.
From onscren material we can gather that the Enterprise
-B was launched in 2293 (the once every 39 years appearance of the Nexus would match up perfectly with Picard and the gang 78 years later in 2371). McCoy's statement that he'd been CMO of the Enterprise
for 27 years would also make Star Trek VI being in 2293 fit nicely too since it would make his start in 2266, so that's another possibility.