[Twan]

Hum yes I translated early game by expansion/rush (with say level 3 max magic researched). Midgame by when you have several schools at levels 4-6. Late when you have several levels 7-9. Also I value more mass astral spells than midgame ones, even if the two are powerful, my Arco's peak would be just in the beginning of late stage, when first level 8-9 battle magic (will of the fates, master enslave) is reached.

But my interpretation is probably not the best as I feel like a note is missing for after.

The end game (when you and all your opponents have most schools at level 9 and access to numerous tartarians able to cast spells like rain of stones) is very different than the beginning of late game, as human mages lose most of their offensive power. On the other hand calling "midgame" all the game between level 4-5 magic and the moment all magic is researched, would make hard to differenciate nations.