Looking at "East African and Abyssinian Campaigns" by Neil Orpen & "A Gathering of Eagles" by James Ambrose Brown, I find nothing on Jackson that you have not already noted
Some additional info on Human from "Springbok Fighter Victory - Vol1" by Michael Schoeman.
Quote:
HUMAN, Colonel Johan Daniel Wilhelm "Johnny" 103021V DSO 20.3.45 DFC 7.3.41 & bar 28.7.42 MiD 24.9.41. Score 5-0-1/2. Born 27.8.13. Alexandria, CP. UATG wings 22.12.39. PF.40 (TacR) Sqdn 1940-41 (174.40 op hrs, 77 sorties). 5 Sqdn 1941-17.3.42 (21 op hrs, 12 sorties). 2 Sqdn 17.3.42-29.7.42, as B Flt cdr then Sqdn OC from 25.5.42. 233 Wing Staff. 5 Sqdn supernumerary 1943. 7 Wing sweep leader 9.5.43-7..43. 7 Wing OC by 5.44-7.4.45 OTE. OC 11 OTU. Formed Comair with A.C. Joubert, J.M.S. Martin, etc, in 1946