A report written for Demand Progress by foremost NSA wonk Marcy Wheeler compiles a 12-year run of NSA overcollection and underreporting. These findings are summarized (lol) in a couple-thousand-word piece Wheeler wrote for Motherboard. Either route you take, you‘ll see the NSA has been given a long leash by its overseers. The end result of this mostly hands-off approach speaks for itself. From the Demand Progress white paper [PDF]:

„For almost 12 years, both under Section 702 and other programs before it, NSA was always engaging in or retaining some kind of electronic surveillance the FISC would go on to deem unauthorized, and NSA would only fix the problem when threatened with criminal sanctions.“