If they would have had an encounter on 23rd, than it might have been mentioned in the war diary of Jagdgeschwader I.
But all it mentiones is that victory of Lt. Wüsthoff (Jasta 4) at 4.50 pm. On that day there took place some 43 (Kriegsflüge) combat flights. Maybe they met on one of these? But however, I doubt it was a Fokker Triplane. * :
Rittmeister von Richthofen flew
one of the new (quotation from JG I war diary) Fokker triplanes on September 1st and downed his 60th, an British artillery spotter who took him obviously for one of the Sopwith triplanes since he made no attempt to defence himself. Obviously there was a lot of confusion. And do not forgett about all the other triplanes around in those days. I do not know when the first front line trials of the Pfalz Dr.I took place, but they might have been around these days, too.
Achim
P.S. Dan-San (below) is right about the Pfalz Dr.I since Idflieg orderd some 10 of tese by October first time for evaluation.(just checked

)