Anytime I get about midway through a game of Civilization V, the military advisor stops giving me information about how strong most of my opponents are. That is, at the start of the game he will say something like:
The Ottomans wield an empire that could wipe us off the face of the planet
The Chinese aren't quite as strong as us militarily
He will initially provide this information about each other player. This is useful information, but later in the game he only provides it for some other players, not all. Why is this? Also, what determines when he will stop providing this information?