That' exactly my point Wolf. You describe them as witnesses. But the very first one is no such thing.
But I got interested in the "Ubatuba Magnesium Mystery" (nice name Ubatuba, a strange and mysterious name, don't you think)
And I found this:
from
http://www.magonia.demon.co.uk/arc/70/ubatuba.html
"However, according to the Condon Report, a check was made of Dow Metallurgical Laboratory records and revealed that the company had made experimental batches of magnesium containing various proportions of strontium. As early as 1940 it had produced a 700 gm batch of magnesium containing nominally the same concentration of strontium as was observed in the Ubatuba sample. The Project's conclusion was that there was nothing unique or unearthly in the composition of the Ubatuba fragments and there was thus no reason to suppose that they were of extraterrestrial origin"
and
"That the material is not 100 percent pure magnesium does not lessen the impact of the case, for we still have to explain how that magnesium got to a remote beach area at that time. What manner of machine was the shiny disc-shaped object that exploded?
We do not, in fact, have to explain anything of the sort, as there is no convincing evidence that the samples came from a flying disc, or that they were picked up from a beach, at Ubatuba, or anywhere else. The samples first came to light in the office of a Rio society columnist, where they arrived through the post. The writer of the letter accompanying the samples and his alleged fellow witnesses to the UFO sighting have never been traced.
The more rational conclusion in this case is, plainly, that the Ubatuba affair was a hoax. It must be regarded as one of the most successful hoaxes in the history of ufology, in view of the time and money spent and the amount of technical expertise lavished on it."