For "Yesterday's Enterprise," they couldn't use Vor'chas or Negh'Vars because the dialog explicitly stated that the attacking ships were K'Vort class. Therefore if any CGI updating were to be done, a new ship type would have to be created.
Not necessarily. This is an alternate universe, after all - the name K'Vort
could apply to either of those existing modern designs in that universe.
We already have to accept that the alternate universe Klingons name their ships differently. The very footage of the K'Vort
attack from "Yesterday's Enterprise
" is used in "Rascals" to describe the attack of a pair of ships explicated as B'Rel
class. And there's no way those two could be as small as Martok's Rotarran
, as we see a number of scenes where the two assailants surround the hero ship and demonstrate their considerable size.
Basically, that's bad news for the publication... And didn't we already see a background graphic in DS9 that referred to Martok's ship as being of the K'Vort