As far as I can tell it is goes by Date of last activity. That's why they say not to pay after collection.
I'm pretty sure anyway. Someone else feel free to correct me. I'm still learning!
10/2007 TU 545 EX 538 EQ 529
2/2008 TU 628 EX 608 EQ 587
3/2008 TU 636 EX 627 EQ 613
4/2008 TU 637 EX 618 EQ 621