It's canon
The Steamrunner and the Sabre are warships, not explorers, also they are designs from the 2360s at the very earliest and so are not around yet by the Lost Era.
I know this is only the conjectural history from the ASDB site but their designs for unseen ships are very cool, they did the TOS Antares that Lord Schtupp was doing ages ago but never finished. In their version at least, not sure if they got facts from the show but:
First commissioned 2320
The Korolev Class is a widely-used, yet seldom-seen starship. Production was in full swing in 2330, as a smaller counterpart to the still-new Ambassador Class. A number of Korolevs saw their operational lives abruptly terminated in the Borg incursion of 2367, at the Battle of Wolf 359. Though most have been refit, and can more than hold their own, recent years have seen them largely assigned to the Federation's territory in Beta Quadrant.
So one of these could very nicely fill the role for that era, plus their design looks very nifty (that means good)
http://www.trekships.org/korolev-redesign-side.jpgTragically there's only this view of the design at the moment. I think they also did the Ambassador-esque Rennaisance design, without resorting to a really crappy kitbash like the one I saw on shipschematics.