I wrote a little about this on the other test server, so I've snagged my thoughts from there.
Spoilers here for Book 14! Don't read on unless you want to see spoilers!
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Concerning the change in the timing: it's a bigger change than we generally make, it's true, but after a good deal of consideration I think it makes a certain amount of videogame sense:
+ It makes the search for Lothrandir easier to motivate
+ Since this Volume was very much the story of the Grey Company, it's good to involve them in the closing chapters beyond having them show up only in an Epilogue or during the last chapter and being done with them
+ There isn't a great deal that is changed by having them show up early: the information they bring probably doesn't change Gandalf's upcoming decision, and since in our version they share an aim with Aragorn and co. (involving the resolution of Saruman's threat), it makes sense that they would come along.
+ It lets me do one of the Inside Baseball-type chapter titles that give me the giggles: 'Allies Unexpected' could refer to the Ents showing up after the Battle of the Hornburg... or it could refer to the Grey Company, who fans of the book *really* don't expect to see this early.
So it *is* a change, but I think it's a justifiable one for our purposes.
MoL