^ Yep. Tikopai and Achernar were both referenced by FASA because they were previously mentioned by FJ, and the FYW supplement even has a fictional contributor named after him. Whether or not that means FASA intended them to be Constitution subclasses as FJ intended or to be alternate designs that perhaps looked different (FASA claimed they had "unusual" designs, but didn't give any context for that) isn't clear. FASA says the Constitutions themselves were withdrawn from the front lines after the first year of the war, because they were considered the most advanced Federation vessels at the time and Starfleet didn't want to risk them being captured by Klingon forces.
As far as the timeline goes, FASA's chronology (itself based on the earlier - and now highly inaccurate - Spaceflight Chronology) is off from the canonical one by a good five or six decades I believe - the Enterprise's five year mission under Kirk took place from 2207 to 2212, far earlier than the later dates introduced officially. Since the first source to give any canonical time reference was TWOK, and then only that it was set in the 23rd century, this isn't too surprising. The FYW would have been earlier than Kirk's command, since Garth won his reputation for actions at Axanar and the conflict led to the cold war atmosphere of the TOS era.