Has that "half-written" story been published anywhere?
You've got some good hard questions that I don't think I have good answers
for. Nevertheless:
A. Kocher's points about specific items in Giles seem on the mark
to me; only his assumption that it was written (see also my response to
question D) as a post-effort release was wrong.
B. The Silmarillion is such an all-encompassing fairy-tale
prehistory of our world that Tolkien, with so many possibilities and
resonances, that it would be hard for his other work not to lead back to it.
C. Sort of an anti-escape escape, isn't it? Like a vacation from a
vacation.
D. I wonder if Unwin was thinking along Kocher's lines here: don't
publish the minor comic work till he finishes the major serious work; don't let
him relax.
Two other items:
1. I note that in Letter 122, Tolkien appears to answer Kocher's question
on who wrote the blunderbuss definition: A.H. Murray.
2. "Obviously this is an embarrassing sort of weapon to own when a dragon
named Chrysophylax Dives, 'cunning, inquisitive, greedy, well-armoured but not
over bold,' invades the kingdom after a hard winter, particularly for Giles who
is not overbold himself." Is that right, about the "hard winter?"
Didn't the dragon appear a little before Christmas, in the
fall?