Later that year, the Constantinople underwent a colonization mission transporting 2,012 colonists. During the mission, the ship suffered a major hull breach compromising their environmental system. Fortunately, their distress call was received by the nearby USS Enterprise-D, which was on its way to the nearby planet Gravesworld. The ship was repaired and the 46 minor injuries treated. The Enterprise also left medical supplies before continuing to Gravesworld. (TNG: "The Schizoid Man")
Later that year, the Constantinople was on special assignment for Terraform Command. The ship was named on the Starship Deploy Status chart in the Starbase 173 courtroom. (TNG: "The Measure Of A Man", okudagram)
The registry was derived from the Starship Deploy Status chart seen in "The Measure of a Man".
This association between the Constantinople and the class and registry were picked up later by the Star Trek Encyclopedia (4th ed., vol. 1, p. 158), where it was said that the starship was "named for the Turkish city also known as Istanbul."