On the evening of January 23, 1974, residents of the Berwyn Mountains area in northern Wales reported a loud noise and a bright light in the sky.

This case matters because it is a documented mass event whose object identity remains unresolved.
Documented
On the evening of January 23, 1974, residents of the Berwyn Mountains area in northern Wales reported a loud noise and a bright light in the sky.
Debated
The identity of the object
Debated
The adequacy of the conventional explanation
Unverified
Extraterrestrial origin
Unverified
Any claim stronger than the record supports
Unverified
That a crash or retrieval ("Welsh Roswell") occurred
Sources are kept in separate layers: official and contemporary material is documented; secondary UFO literature is treated as debated, not as primary evidence.
Secondary / debated material.
Documented source.
Documented source.