Ulrich
It's a really good course and the greens aren't flat at all. Don't expect big dunes, but the land is nicely rumpled.
There's quite a lot wrong on the website history. Colt built the 36 hole complex on the current site but it has been changed a fair amount. From a stick diagram drawn in the 1920s, I estimate about 60% of the routing is original.
The website is correct that a third course (also Colt and Alison) at Letterbek was lost during the war.
I know Colt worked on the original Knokke course, on a different site, but 1907 seems early.
I'm not sure how Allen was involved perhaps he was responsible for the redesign of the 36, after WW2.