Michael,
I suspected you had a good "hole card"- nice research!
Olson's writings support the gas escape theory with clip loading secondary, while Otteson and Dehaas go with clip loading primary and gas escape secondary.
In the FI ads announcing the new FN actions availability in the late '40s they stated "thumb-recess eliminated" among the features. Does this mean it was no longer needed, or wasn't a big deal anymore?
FYI, I have one of the very early post-war FNs. The bolt ports still exit the left raceway.
From reading the responses, it appears that very few of us have shot NRA High Power with a bolt gun.
Good shooting.
