True patterns exist. However, they are not the ones who the fandom mentions frequently.
This is are example of "fan-made patterns":
-Ash always catch the flying type.
-Ash's flyuer always evolve.
-Ash's water type never evolves.
-Ash will always get a grass type.
-Ash is going to lost exactly one Gym leader per saga.
-Clemont is going to get 3 pokemon.
-Passive females are going to get 4 Pokemon.
-The most recent female companion is going to cameo.
-Because Ash hasn't have the 3 starters, Ash's starter is going to evolve.
-Even number gens doesn't have a "filler" saga.
-Because a female has a Pokedex, they are going to get an active goal.
-The main cast can't catch 3rd stage Pokemon or pokemon that evolves through stone, "trade", item + "trade".
-Ash won't rotate his team.
-Villain teams are going to appear in the first year of a series.
-Companions never get to battle Gym Leaders.
And now I will show examples of "true patterns":
-A movie is going to premeire in mid-July.
-We never get episodes the week of New Year.
-A saga starts when the first pair of games are released.
-Pikachu is not going to evolve into Raichu.
-For new sagas, they will be new companions to promote the games.
-A Character that leaves is not going to return.
-There aren't main cast changes in the middle of a saga.
-The main cast is not going to get super-legendaries (Kyogre, Dialga, Yveltal) and the cast is not going to get legendaries in the long term.