: These cartridges and their ROMs are bootleg products, often created by third-party companies without Nintendo's authorization. Game Quality & Repetition
Most individual NES games were tiny—some as small as 40 Kilobytes . By stripping out intros or credits, bootleggers could cram dozens of these small files into a single large ROM. 300 in 1 nes rom
Some versions include titles from manufacturers like Sachen (e.g., Jewelry ) or Nice Code. : These cartridges and their ROMs are bootleg
But not for the reasons you think.