Since ListMailPRO stores the Seq # of the next followup to send, the code would be correct if you want to send to people on list 1 who have received follow ups 9, 10, and 11 and will receive follow ups 10, 11 and 12 next.
From the looks of the brackets it appears you may have set up your User Selection rules in sub-levels.
You can add all rules on the same level. ie:
NOT:
Active List 1 Seq 10
+ OR Seq 11
- + OR Seq 12
BUT:
Active List 1 Seq 10
OR Seq 11
OR Seq 12
Regards