The J is in the 26th century regardless of where the E was in its timeline. It still tells us something of the longevity of Starfleet legacy numbering, and possible spacing. Applying the J's spacing (about 2.3 letters including a Nil, from every century), then the Yelchin-E might coincidentally date to around the early 26th century.
More likely, of course, there are large gaps and/or large service histories of the Yelchins and it was probably a 30th or 31st century launch.
It’s the 26th century of a different timeline that changed from the 22nd century onward. Again, it’s not germane to the discussion.