No ye series hai. Matlab jab se ghusna hai ghus jao. But you will have to pay for all coming exams after u entered in between.
But its ur wish that if u just want to give open tests only so give open only. Leave all. But u will have to pay for all remaining exams.
But my advice would be enter after pt3 as open test wale mein kam exams hain and money diff is very less.