The Winning Conditions are described at pg. 11.
An Economic Victory includes (only) the Combined IPC Level for all Nations of the same alliance on the Expanded National Production Chart (ENPC).
Any IPC that are collected according to Advanced Production Capacity and National Objective Bonus Income do not count towards the Economic Victory Conditions.
Example:
When the US player captures Caroline Islands, the US player’s IPC Income Level is increased with 3 IPC at the Expanded National Production Chart- and Japan’s IPC Level is decreased with 3 IPC accordingly.
The US IPC increase at 3 IPC naturally counts towards the Economic Victory Conditions.