To avoid mass ontological shock and cognitive dissonance causing a partial collapse scenario, they're extraordinarily slowly spreading out Disclosure over many decades. We'll likely be 20-30 years older before much more significant info is released.
Most of the major themes and high-level ideas about what we know today about UAP's was already known by approximately 1958. The terminology is different, and in '58 only a tiny collection of dedicated researchers knew about some of the wilder stuff. Very little new has surfaced.
In many ways we actually know less about the phenomenon than researchers and even the general public knew in the 50's.
The "Working Group" kept the subject of UAP's and C/R's (Crash Retrievals) in the public eye for decades: Dr. Edward Teller created Lazar in the 80's. And Dr. Vannevar Bush pushed his associates from the war to help reveal the Aztec C/R to Scully.
There's no longer a need to classify C/R's (Crash Retrievals) because all the major powers (Russia, China, and the US) each have had their share of crashes now (Dr. Davis). The subject naturally tends to keep itself secret because few understand it, or can handle it. #ufotwitter
This allows the US, for example, to recruit for the CRP (Crash Retrieval Program - again Dr. Davis) right in the open! They can even put the declassification announcement right in NY Times. Still, basically nobody gets it yet - even people on ufotwitter.
Cognitive Dissonance is so powerful that the NatSec state can depend on it to keep the situation relatively calm while they recruit more engineers & scientists with security clearances to examine the retrieved debris and attempt to back-engineer it.
The supposed Roswell craft (illustrated by Kevil D. Randle and others) looks totally badass. I could see this shape being quite inspirational to aircraft engineers in the late 40's/50's. (Thanks @xExist)
The American Heritage Center has sent us more late 40's/early 1950's-era archive scans from their Frank Scully collection. There was a collection of photographic negatives in one box. Here's the first negative (which I inverted), from April 4, 1950:
I find it curious that Proximity Fuzes were being tested close to Socorro, NM in the 40's-50's, a location with many 20th century UAP sightings. Astronomer and ufologist J. Allen Hynek was one of the developers of this super high tech device.
"During World War II, Hynek was a civilian scientist at the Johns Hopkins Applied Physics Laboratory, where he helped to develop the United States Navy's radio proximity fuze.":
These super top secret devices helped us turn the tide during WW2. They amplified the effectiveness of our air defense rounds by roughly 10x. A total game changer. We were afraid to use them during WW2 - we didn't want the Nazis to get samples to back engineer.