Present perfect and past simple

«IN THE COURSE of writing this book I have been fortunate to receive the assistance of a great number of people. During my research I benefited from the generous hospitality and knowledge of Dr Christoph Maier in Basel and Professor Isin Demirkent and Dr Ebru Altan in Istanbul, and the organisational help of Fusun Ersak and Claire Lillywhite-Pinch.»

Dear native speakers, could you please explain the use of present perfect? Obviously the author speakes about the past ( in the course of writing ). And then he switches to past simple, though obviously he means the same timeline. Would be great if someone explained this nuances, as I have noticed that books written by non -native -speakers , incredibly written though they may be, lack this delicate use of present Perfect.