so far i believe, you wanted to ask if you ever have to inform your school about your status in and around 90th days of your OPT start date. If so, the answer is YES. It can be done in many ways depending on the school. Some school set up different login account to know if you are employed or not. However most school (usually international student office) send you an email asking what you are doing. So best thing to do is to keep checking your school email even though you graduated. If none of these things exist, then it's better to email coordinator/or officer telling what you are doing in about day 80. That would be fine.