Reading the appreciation, I got sidetracked after seeing the crosstable for the 1963 Niemeyer tournament and seeing that for whatever reason one of the competitors didn't have a flag against their name (though he has one
here).
I'd not heard of Ernst Roscam Abbing (or any of the competitors except the first two) but hunting around I came across this
page which appears to be a list of champions of the Benoordenhout chess club and which also appears to show that in 2018 Ernst Roscam Abbing won the club championship for the first time.
Now I have no Dutch so I may have misinterpreted the page, but if I'm correct - is there not something very unusual about a player winning their club championship, in their mid-seventies, for the very first time?