Ok. So basically what happens is the score does not get locked after ITA and any change in circumstances such as a birthday can reduce your score. However, if you have a birthday after ITA and your score reduces because of that then this will not cause a rejection of your application. Birthday after ITA is the only thing for which a candidate is not penalized. So the officer will mention on notes that there is point reduction, however the policy is it ignore this in case of birthdays after ITA. So in essence your application will not be rejected if your points decrease because of birthday after ITA. This is clearly mentioned on the invite letter you would have received.