2245 represents a logical extrapolation that allows for both the events of The Cage and having time for a Robert April command that was alluded to in The Counter-Clock Incident working backwards from the 2364 date.
But The Counter-Clock Incident only says that April has been an ambassador for 20 years, it is just an assumption that his ambassadorship started immediately following his tour on the Enterprise. As you say, it is a logical extrapolation, but it isn't the only one. The only mention of the Enterprises age is in TSFS ("The Enterprise is 20 years old") and it is hard to reconcile with other data points.
April could have commanded the 1701 from 2230-35 and then been transferred to another command. The ship was captained by two or three other captains, then he--like Kirk--returned to command the ship again in 2245, this time as a commodore. After that second tour he became an Ambassador at large and transferred command to Chris Pike.
Are the chronologies/encyclopedia's perfect? No. But in the broad strokes they work well enough.
This I would agree with. I don't agree with all the assumptions and conclusions Mike Okuda made, but I have no ill will toward him because of it.
"Canon is only important to certain people because they have to cling to their knowledge of the minutiae. Open your mind! Be a Star Trek fan and open your mind and say, 'Where does Star Trek want to take me now'." - Leonard Nimoy