If you have logging enabled, FMC will store Connection Events. However it has a limited amount of storage. For instance, an FMCv can store 10 million events which can fill up in a day or less on a moderately sized deployment. For long term retention of data, we typically advise something like cloud-delivered FMC (can get 90 days or more of storage - at a price) or sending Netflow data to an external system.
