The seeming problem here is that the Concordia seems to follow the 'carrier' designation sequence - CV with an 'S' dropped down after to signify "dreadnaught". Five ships later the Vesuvius pulls a reset of the system - CV-70 and -71 become CV-01 and CV-02 (to be fair, this apparently did not last long, as by 2701 the TCS Eisen is referred to as "CV-74") and then the Midways decide to go for their own independent numbering scheme and start over - CVX. It seems, in this scenario, that the slots from 66 to 69 have long been filled.
The other possibility is of course that the Confederation has, in fact, built 64 dreadnaughts (or ships classified as dreadnaughts) prior to the Concordia, which is certainly more than possible, of course (but my gut feeling about it is that it is wrong - the American naval scheme Origin was following in 1991 uses the modifier letter to designation different types of carriers while keeping the numbering sequence intact, a sequence all fleet carriers followed.
―with the exception of the CVEs - escort carriers, "supporting carriers" not meant to operate as part of a carrier strike force and in the historical timeline operated under sovereignty of the Army. The novels appear to follow this by declaring the Tarawa CVE-08. To this, however, must be added that the 'Claw (CV-07) was commisioned in 2642, and that unless she bears her designation from a time where she was laid down some time after 2619, lay on the stocks for twenty-odd years and then was finally commisioned (which would explain the Tigerclaw / Tiger's Claw bug addresed in Star Soldier) her number sequence is totally out of whack with the Victory, CV-40 (as a final point, a light carrier) which is very definitely older.
...which brings the final disqualifier: If the ship on the cover of WCII is to be taken as part of the continuity (which it usually is), we have a Confederation-type ship numbered "14", which would go well with the Tiger's Claw but not the Concordia's final designation. (The Concordia was not, at least, the only ship of her class; Kilrathi Saga's manual makes reference to several other ships of the type.)