Chocolate Box Gift Exchange

The Power Rangers TV show is all in continuity with each other. There is an ongoing narrative that goes from Mighty Morphin', Alien Rangers, Zeo, Turbo, and ends in In Space. Lost Galaxy is heavily impacted by the events of past seasons up to the point that their pink ranger dies and is replaced by the previous season's redeemed big bad. Zeo, In Space, Lost Galaxy, Lightspeed Rescue, Time Force, Wild Force, Dino Thunder, and SPD all feature a team up with a previous season's team. Mystic Force's big good the Magic Mother is a redeemed Rita Repulsa from the Mighty Morphin-In Space era. Wild Force brings back all previous red rangers except Rocky. Operation Overdrive brings back a team of five different rangers each from a different season. Bulk is brought back as a character in Samurai along with Spike, who is supposed to be the son of Skull from earlier seasons. Clash of the Red Rangers establishes that there is a multiverse. The powers of the second half of Megaforce are basically using all the powers of the previous seasons and culminates in a battle with every single Power Ranger from the history of the franchise participating, with the red rangers from Samurai and Jungle Fury providing some guidance to the team. Ninja Steel brings back assorted rangers from throughout the history of the franchise to fight off an invading army from another dimension.

Power Rangers isn't like Super Sentai with having each season being its own universe. It's a shared, ongoing universe with a lot of history and built up mythology. Stuff like the morphing grid doesn't have to be answered each season because it had already been established in previous seasons.