Original sentence: During the Belgian UFO Wave, from 1989 to 1991, the SOBEPS (a Belgian ufology group in favor of the extraterrestrial hypothesis) claims there were around 2000 witnesses in all.Most of them were just phone calls given to the SOBEPS office in Brussels and didn't have any further - and proper - investigations.On the first night of the wave, November 29, 1989, 143 sightings were recorded, according to the SOBEPS.On the night of 30/31 March 1990, unknown objects were tracked on radar.On top of that, most of the phone calls were not recorded or archived.This night was the peak of the Belgian UFO Wave in terms of ground sightings
Edited sentence: On that night unknown objects were tracked on radar, photographed, and were sighted by an estimated 13,500 people on the ground - 2,600 of whom filed written statements describing in detail what they had seen.The Belgian UFO wave peaked with the events of the night of 30/31 March 1990