I read on their website, at the point of your e-PR submission, if you CRS score becomes below than the lowest invitation one (e.g. you pass your birthdate during the application preparation), your invitation might be withdrawn and you need to submit an explanation letter.
Correct me if I am wrong. I hope I'm wrong, actually; I don't mean to make you worried. But if this is true, you might want to prepare most to all of the required documents and submit your application as soon as you receive your ITA. This is what I will do too.