Commander Maxillius your information is incorrect, the Mogai class Type of Romulan Warbird which predated the D'deridex class but came after the C-10 class. Several Mogai class Warbirds were used to hunt for the Norexan when Romulan senior figures learned of its planned defection. The class was only used as a reserve type during the Dominion War and not on the front-lines. ["On Duranium Wings" (IST)
Mogai Class
(See Attached Photo)
Reguarding the Valdore ......
The ship's official class designation is unknown: it is listed in the customisable card game as the Norexan-class (Valdore being the name of an individual ship), whilst the Star Trek: Titan novels identify the frame as Mogai class; however, none of the three names have been confirmed onscreen. Due to the named onscreen vessel Valdore, this is how the class is most commonly known.
And finally some more Romulan facts ...........
-No Romulan ship has ever been identified on live-action screen as a "Bird Of Prey." Lieutenant Stiles stated in TOS episode Balance of Terror that the ship was "painted like a large bird-of-prey." The terms "Romulan Bird of Prey" is therefore a fanon term, as it has not been cannonically referred to as such by Paramount.
-The Bird of Prey ship seen in the TOS episode Balance of Terror was mentioned by Scotty to be powered only by simple impulse. This is usually interpreted as a sublight-only capable ship. This has led many, including game designers for the Star Fleet Universe to assume that Romulan ships had no warp capability at this time. Since there would be no reason to use an obsolete ship for such a mission, this would mean that the Romulans had no warp drive prior to the Klingon-Romulan alliance. As a result, however, the Romulan war fought in the 22nd century would not have been possible unless Earth took the war to them. It would also mean that it would have taken the Bird of Prey seen in Balance of Terror a lifetime to cross the neutral zone, let alone journey to the several outposts that line it. Therefore, Scotty's line has had a number of fanon reinterpretations. In later episodes of Star Trek: The Next Generation, we learn that Romulan engines use artificial black holes as a power source; it is most likely that Scotty, not knowing of such technology, assumed that this Romulan ship did not have warp drive when it in fact did have it (the vessel clearly moves at faster than light speeds in the episode; this would be impossible without some form of warp drive).
-During the Dominion War, the Romulan flagship was the D'ridthau. Its class is unknown, although (given its name, and its status as fleet flagship) it may have been a Warbird (D'deridex-class), or of a new class. It never appeared onscreen, but in the episode "What You Leave Behind" the D'ridthau was destroyed in battle by the Dominion.