This is becoming clearer.
My read of this is that "A" was coming clear of a buoyed channel into an
"open" stretch of water when it met "B" and the subsequent collision
occurred in the "open" stretch of water (Inland Rules in force), not the
buoyed channel. (still not 100% sure on this, but g close)
Of the CG findings:
a,b,c, no problem.
d G Unless you're a military vessel, having extra hands to take
compass bearings, other than eyeball, and the value of them if vessels
are not maintaining course is interpretive, but this is a rule 2 "gotcha".
e debatable, but, understandable.

In answer to your feelings regarding the vessel entering the channel
from the side .... It is going to depend on the exact location of the
meeting. If the two vessels will be meeting IN the buoyed channel, then
that vessel (entering) will be required not to impede the vessel in the
channel. However if the meeting will occur in the approaches to the
channel, then the vessels will have to address the "normal" rules.

As to the proposal/acceptance aspect. Although I can see the courts
stepped decision regarding which rules take priority when assessing
blame (you haven't stated how much "B" was held liable and for what), I
would argue that at the point that the 2 blast signals where exchanged,
this became in effect a passing situation with everyone in agreement and
now both vessels should be maneuvering under that agreement .... and
here, this goes to possible responsibility on "B".

otn