It was the journalist WILLIAM "Bill" BEQUETTE, from United Press, who had the bad idea of creating the phrase "flying saucers” because he confused the flight dynamics described by Kenneth Arnold, with the shape of the objects he sighted.
The acronym has the virtue of being read as YouFoe (you enemy) attending to the quintessence of the interest of the BlueBook, which collected all reports of sightings of something strange, but which was really interested in determining if USSR planes or missiles had crossed the sky of the USA.
Ruppelt, after the closing of the Blue Book, wrote a book entitled "The Report on Unidentified Flying Objects" in 1956, that is essentially testimonial, and ends by raising the question of whether UFOs really exist or not, to which he comments: "Time will tell ".
But after a while, Ruppelt wrote a second book, the text of which I know about in a publication made in 2012 under the title "The Uncensored Truth About UFOs". That book contains a second author, Chet Dembeck, with an addition of 40 pages (549 to 589) that frankly should never have been added.
In this second instance, Ruppelt wrote culminating with the following: "I am going to go beyond the Air Force, however, and quote a letter from ex-Lieutenant Andy Flues, who was a researcher for Project Blue Book. The statement of Flues sums up what I believe , I'm sure, the beliefs of everyone who ever worked on the Sign, Grudge, or Blue Book Projects."
Flues wrote: "Even taking into account the highly qualified backgrounds of some people who made observations, there was not a single case which, after close analysis, could not be logically explained in terms of some common object or phenomenon."
And this observation of Lt. Flues is still valid for a very high percentage of what is still denounced as U.A.P., except that they possibly are sophisticated espionage devices, they are not common objects, although they can finally be fully identified.
Meanwhile, an "unidentified" is anything that someone could not identify at the time of making the observation, or later seeing a photo or video, of something that was not seen at the time but was captured by their camera.
But the misunderstanding with the designation of something "unidentified" came to a head when referring to the Chinese balloon that flew over the United States until it was shot down because it was spoken of as "unidentified". It was enough that it was a balloon identified as such, so that the category of "unidentified" did not apply. Not even for the other two balloons.