It's a simple thing...What happens if you inform USCIS right away and they hit you with "give us the divorce certificate" yet you don't have it.
When that happens, you just made their life easy and yours difficult....denial. And they'll be right at denying you.
You only have limited time to respond to an RFE, beyond which is a denial.
Problem is when someone files joint ROC, get the divorce certificate before ROC is adjudicated and keeps quiet. Come N400, you'll be caught and sent back to properly redo ROC. There was a post here earlier this year of this very same situation. Maybe @Redro can dig VJ archives for it.
My 3 bullet points also apply for your case, which I know very well. Unfortunately, that's all I'll tell you. You've already received a plethora of advices.