I've been told that even some authorized arcade emulator releases actually use bootleg MAME sets because they lost the original code that ran in the "protection

I've been told that even some authorized arcade emulator releases actually use bootleg MAME sets because they lost the original code that ran in the "protection MCU". If you don't know what that is: to delay bootleg production, arcade vendors used to put some bit of important code inside a microcontroller, so that just copying the ROM chips produced a broken game and bootleg vendors would have to reverse engineer it and reproduce it in the main CPU program, sometimes leading to gameplay differences (IIRC, the generation of the "EXTEND" bubbles in Bubble Bobble was an example noticeable to expert players).