During the NES era, Nintendo maintained exclusive control over titles released for the system—the company had to approve every game, each third-party developer could only release up to five games per year (but some third parties got around this by using different names, for example Konami's "Ultra Games" brand), those games could not be released on another console within two years, and Nintendo was the exclusive manufacturer and supplier of NES cartridges. For how many years did Nintendo require exclusivity on NES games