>>58156237
You probably didn't notice this as a kid, especially since the anime in Japan has far more cross-media synergy than it did in the west, but during AG, they just immediately pivot to FRLG content right around the time they do the Norman rematch. The opening changes to feature Gen I Pokémon like the fully evolved Kanto starters, there's immediately an episode with Professor Oak and the first stage Kanto starters, May gets a Bulbasaur, Squirtle and Eevee, Ash's Charizard comes back, they decide to travel through Kanto after the Hoenn League, the Deoxys movie features its Attack and Defense Formes, etc.
Emerald content starts happening around the later badges. Juan appears instead of Wallace, there's an episode about Deoxys Speed Forme, Rayquaza is a prominent Pokémon in the Deoxys movie, Mew being featured in the next movie, Scott is introduced and the story changes to doing the Battle Frontier, etc. And a lot of this runs concurrently to the FRLG stuff (which started before it). And then, of course, there's all the DP promotional stuff like Munchlax appearing in the Deoxys movie, May getting a Munchlax, Brock getting a Bonsly, James getting a Mime Jr., the Aipom following Ash around because it's getting an evolution in DP, the Lucario movie that also featured Weavile, the Manaphy movie that also had Buizel, Mantyke, and Chatot, etc