So...Somethings we know from comments on the stuff in the Dark Age is that OmniMechs were part of the "signature aesthetic" of the Nova Cats. It was implied that most other groups had stpped making OmniMechs, in fact, the Novas we saw were supposedly no-longer OmniMechs.
You're reading to much into a half remembered paragraph. The exact quote (and you dont know HOW hard it was to find
a copy of it) follows.
Before concepting and sculpting a new faction, an internal style guide is first generated. MechWarrior Digital Studio Manager Vic Bonilla reviews source materials here in the office and then generates a style guide based in part on those findings as well as input from the game designer and other sculptors. From the style guide comes what are referred to as the key elements of a faction. The key elements of Clan Nova Cat are:
Mystical elements. *snip*
OmniMech technology. In part because of their affinity for OmniMechs (BattleMechs with interchangeable parts), Nova Cat units have an overall look and feel to them.
Neo-Gothic Elements. *snip*
No where in there does it hint that the Nova Cats are the only ones still producing Omnis. At worse, it implies that the Nova Cats might have a higher ratio of Omnis to Non Omnis then other factions.
As is, there's plenty of evidence of Omni use into the DAs.
Karhu Omnis are mentioned being used by the Ghost Bears. (It's where we first spotted it)
There's the Mad Cat IV and Vulture IV, both new Omnis.
From Tammi Miller's FP dossier "Vultures were a common sight among the invading Clans, particularly in the Ghost Bear and Smoke Jaguar armies, and remain so
even today."
From Noel Hurtato's dossier: "Because of its significance to its touman, the Falcon made a point of adding production lines for the Thor to its Sudeten BattleMech factories, ensuring the continued deployment of this machine even after home world ties were severed." This line was later mentioned in Master's and Minions.
Multiple Vulture and Summoner dossiers list parts (Olivetti T4 Endo-steel, Bergan Version 8.3 Endo Steel) made in IS located Clan facilities. While circumstantial (it could also just be signs of a standardised refit), this could be used to show newer Omnis produced from that facility.