Well I think the Concordia class is a little more than just a retrofitted Yorktown (official name for the old Ranger-class)
After all, Eisen mentioned he'd been communications officer on the Victory's maiden voyage. Look how old Eisen is. If we assume he's as old as the actor and he was communications officer aound the age Rollins is, (I don't know if the characters' age was ever mentioned somewhere), then the Victory had her maiden voyage over 30 years before WC3. That puts it pretty much at the beginning of the Kilrathi war. I think the novel mentioned the design itself was a pre-war design even.
So I doubt they retrofitted a 50 year old design at the time of WC4. I think the thing just happens to look about the same, but probably has a totally different internal layout.
We all know it is simply a reused model for the game, but if you want an in-universe explanation, I think after 50 years, more modern armor, more modern structural designs, smaller more effective reactors etc would make more than enough room for additional fighter complements etc.
The sources are very very problematic anyway. Read the WC4 novel. Forstchen totally missunderstood the name "Concordia class" and actually describes the Lexington to be of the same class as the TCS Concordia. Even mentions that Blair is getting the office he knew so well from his time aboard the Concordia when Angel held that office.
So you can pretty much make anything up about the Concordia class. I personally consider it a very new design for a medium fleet carrier that is bigger than the Yorktown and just happens to look similar from the outside but has a radically different internal layout.
That is... when I bother about that at all
which usally isn't the case.
To over-discuss such things makes about as much sense as arguing Star Wars physics (a thing that is not present even according to G.L. himself
)