The "1986" prefix is not a year, but a release number assigned by early ROM scene groups to keep track of their catalog. The "Trashlocke" Phenomenon
After exhaustive research across historical Pokémon release databases, Nintendo archives, and ROM hacking forums (such as PokeCommunity and Whack a Hack),
assigned by the Scene (a global network of groups who rip and share games). It does refer to the year 1986; Pokémon Emerald was actually released in 2004/2005. Pokémon Emerald (U) signifies that this is the USA/North American version of the game. : This is the handle of the ROM dumper
What's the difference between different roms? : r/PokemonROMhacks