Depends on the airline. What airline did you fly on , which route, and what was the fare basis , ie booking code?

Very few airlines' FFP give retroactive credit once flown, but there are a few who do make an exception. Especially the ones that you have to physically send in an application form to get a number(or to process the application with a temporary number).... that way you may write in and say that you HAD submitted the form x weeks ago and haven't heard back yet and you can attribute to it being lost in the mail... etc.