[JYoung]

Exact dates are known about part of the damages.
20 Aug. a Nakajima Type 97 Transport plane: major damage
26 Aug. a Messerschmitt Bf 108: major damage
28 Aug. Two Nakajima-Fokker Super Universals: major damage
At least no casualties were reported in those damages.

Source: Dai ni Hikô Shûdan Shirêbu (2nd Flight Group Head Quarters), “Dai ni ji Nomonhan jiken higa songai ichiranhyô Shôwa 14 nen 9 gatsu 1 nichi (A table of enemy’s and our damages during the Battles of Khalkhyn Gol, 1 September 1939)”, <https://www.jacar.archives.go.jp/aj/meta/reference-en> reference code: C16120576600, (Accessed on 19 April 2017)

Best regards.
JY