Take whatever the FF phone people tell you with a LARGE grain of salt. In my experiemce, they are quite frequently inaccurate even about the current system, let alone the new one. In particular, I find it totally implausible that only tier points accrued after 15/9 will count for tier credits: that would turn the whole thing into a huge lottery dependent on what month your membership starts! There are still 4 months to go until the new system starts; that leaves lots of time for chopping and changing, and I'll bet there will be plenty!