I have just finished reading the second set of documents on the NSA's website. They are "Communication Intelligence (COMINT) reports (broken into sizable parts for viewing.)"
You get a list of parts labelled PART A to PART J. Each part, A to J is 25 pages long and Part J is 16 pages making for a total of 241 pages. These 241 pages consist of fragments of visible text, areas of blacked out text and large area completely white.
I'll give a few examples for your edification:
Page 1 "1355-1401 One UFO. From 75NM E of (blacked out text) toward East and faded near ()"
Page 4 "Message 03787232. Radar tracking UFO 0601-1040 One UFO (probably a balloon) From () toward East and passed north of () South of () Alt 46,000-49,200 ft."
Most of the rest of the pages are similar. They mention anywhere between 1-46 UFOs, and various altitudes between 6,500 and 100,000 feet. No dates are given and almost all location names are blacked out. Usually the acronym "UFO" is followed by the words (probably a balloon.)
After you have digested page after page of UFO/probably a balloon you do get some descriptive sightings. Examples are:
Page 136. UFO 2130Z and 2140Z "Semi circle shape and looked like an arc in the sky. This object was also noted as being white and very large. It was seen for a period of about ten minutes and it seemed to just hang in the sky for a few minutes before moving on in a westerly direction."
Page 137. "() a smoking luminous object that moved through the air at an altitude of approximately 630 metres from () towards() at the border opposite () the smoke radius extended about 100 meters from the centre of the luminous object and a green light could be seen following it. The smoke radius gradually increased in size and disappeared. The luminous object which was in the center of the smoke also disappeared."
Page 224 "Sighted a UFO described as spherical or disc-like in form with established color, brighter than the Sun, with a diameter of one-half the visible size of the Moon.2. At the time of observation, object was above the upper edge of the clouds on true bearing 120 degrees, azimuth 280 degrees traveling north."
Comment: Are these the COMINT reports which the NSA would not release in 1980? Could well be. They really don't tell you much, given that dates and times and places are not usually available. Again, I guess thought, that the NSA is correct in its 21 page secret affidavit (which provides some dates and how the COMINTs were sourced) that if they gave these details out, foreign intelligence agencies might be able to work out what the NSA capabilities were. However, given that the newest document described here in now 30 years old, would it really matter at this point in time?
If you diligently read all 241 pages you will find two names which are not blacked out! Hsinchou and Makung. Hsinchu and Makung are both in Taiwan. One could imagine that either China or Taiwan could have been floating propaganda balloons over the other place and NSA was picking up transmissions about these flights.
I therefore searched the Internet for any references to Taiwan and propaganda balloons and, surprising or not, found an article, published in the year 2000 titled "Taiwan's propaganda cold war:the offshore island crisis of 1954 and 1958" by Gary D Rawnsley. The URL is here
Part of the article reads: "...the CIA Far East Division encouraged the launch from Taiwan of balloons loaded with propaganda leaflets, pamphlets and newspapers that would drift across the strait to the mainland."
A reasonable conclusion, after reading these COMINT documents from the National Security Agency is that many refer to propaganda balloons being flown over China from Taiwan.