Since the 90s, possibly even before that. My uncle went to Hong Kong back in the mid 90s and said there were a ton of bootleg Genesis and SNES games for sale at various shops. When he told me they cost around $10 American dollars each, I got mad at him for not picking me up a few considering the same games were being sold for $60+ in the US lol. But with the internet becoming more of a thing, it has really taken off over the past 10-years or so. It seems like you're just as likely now to come across a fake Pokemon handheld game as you are a real one. I even know several indie game stores that sell fakes along with real copies, given they tell you which is which, but the fakes are like $30 while the real ones are priced according to ebay/pricecharting. It's a really sad state of affairs, not because I'm completely against piracy, but because many people buy the fakes not knowing they've been duped. A few years ago a guy whose in a gaming buy/sell/trade Facebook group I follow sold some of the GBA pokemon games to another member, only to find out that he'd sold him bootleg copies. I believed the guy's sincerity when he said he had no idea. Supposedly he bought them off ebay, thinking they were real. But you really have to be on your guard now since even the labels aren't a dead giveaway like they used to be. Only way to truly tell is if you open it up and look at the board. Same goes for high dollar SNES, Genesis, and NES games too.