April 20, 1918:
A. Hitler's 29th birthdate
A. Hudson's birthday (H's dad)

April 21, 1918:
Baron Manfred von Richthofen 'of the 80 victories' shot down for the last time.

Unfortunately (for me), I'm short on access time and don't have all the information at hand that I'd amassed for my CFS1 April Skies mini-campaign (my accompanying videos listed pilots but only their victory counts; I had that information at hand, though). Just looking at squadron/aircraft can be misleading since Australians and Canadians are often incorporated as 'English' and, more to the fact, American flyers were acknowledged as French prior to the U.S. declaration of war. Manfred's first, and 'unofficial', victories were French planes. At least one of the official Nieuports he shot down, undoubtedly the one to which you refer, was Belgian.

A.D. 1917:
The first time, to my knowledge, that Manfred went down was somewhat of a contention as to the 'shot' down aspect. The Albatros had a weakness in the wing making it susceptible to breakage. A repeat of this occurance with another pilot supposedly led to the development of the Dreidekker. As a note, Richthofen watched the Albatros (DII) of his famed leader, Oswald Boelcke*, rip to pieces on its way down.
Somewhat later he was downed second time. Although, again, unscathed and landed his bullet-wounded plane.
The major incident took him out of action for a while. In a bout with two RCF planes, his skull was shattered by one of their bullets. As on his fatal day a half-year later, he still managed to land; thereafter, however, he suffered frequent headaches and his skill (and skull) was reportedly impaired.
I probably missed something so you can fill in the blanks.

*P.S. Manfred von Richthofen was killed 11 days short of his 26th birthdate (if alive, he'd be 116 a week from this Friday); therefore, he was still the same age as was Boelcke when he died.