It really depends on the area how much they move from summer, fall, and winter. Billies typically only are around nannies for one reason, so in some areas they do move quite a bit late fall. Depending on terrain and snowfall, they may winter in a different area, or may not.
Usually though as a non resident you will not be hunting late. As much as I'd like to get another winter goat, hunting on my own in the MT backcountry during the snow season is not the best idea. Non residents usually hunt early enough that late summer scouting is good for hunting.
As far as books, there are a lot of great hunting books, but the gold standard for goats is probably A Beast the Color of Winter.
I just plan to spend a week in MT each year in August as a scouting/vacation. It's great because it's motivation to keep in goat hunting shape and gets me into goat country each year. My goal is to check out every single drainage in my hunting area and know exactly where I'll hunt if I ever do draw a tag. If I don't draw, I've still had a lot of enjoyment from the process.
This was from last summer:
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