Swiss physicist and balloonist Auguste Piccard reached world altitude records of 15.8 km (51,800 ft) in May 1931 and 16.2 km (53,000 ft) in August 1932, accompanied by Paul Kipfer in the former and by Max Cosyns in the latter flight.

The Wikipedia article writes he ultimately made 27 balloon flights and has gone as high as 23,000 meters (75,500 ft). When did Piccard fly to that altitude, and do you know a list of all his balloon flights?