It has been referred to in passing. In Demons of Air & Darkness (and others) it was stated that Cardassia's remaining fleet was rather pitifully small (barely over a dozen operating Galor-class ships if I recall, many of which were running in states of disrepair).
Where did you get the "one dozen" bit? The Trager
was definitely operating with a lot of damage, though, and as far as I could tell was the ONLY ship the Cardassians were able to spare to help with the Gateways crisis.