Momentum & Flex were basically the same plans.
TurnAround was the program name that included Flex & Core.
Momentum was the re-named program that included two techniques. Counting points (Flex), and simply filling (basically Core). Just a different name.
They're both considered the "older Points" plans. (As opposed to the "new points" plan which is PointsPlus.)
If you still have your materials from Flex you should be perfectly fine in following it.
PS - Welcome to 3FC! Hope to see you around the boards