A lot of sequels follow the usual pattern of just slapping a “2” onto the title of the first film…or at least referencing it in some clever way (see 22 Jump Street or I Still Know What You Did Last Summer)…
…but SOME have entirely NEW titles that don’t connect the movies at all and you wouldn’t even know they were connected unless someone told you, you read about it, or were already in the know somehow.
For example:
Patriot Games and Clear and Present Danger. A movie and its sequel. Hell, I didn’t know about this one until I was in my 30s, despite being 10 when the first one came out.
Another that comes to mind immediately is Pitch Black and The Chronicles of Riddick, …and then we have Chinatown and The Two Jakes. Also Terms of Endearment and The Evening Star.
SPIRITUAL SUCCESSORS do not count, has to be advertised as an actual sequel. So saying “Fierce Creatures is the sequel to A Fish Called Wanda” doesn’t work.
Rankin-Bass’s Return of the King is animated in the style of their version of The Hobbit, and does not obviously follow from Ralph Bakshi’s cleverly rotoscoped Lord of the Rings … although IYKYK.
I want to believe that someone somewhere liked Christian Bale’s other films, but had no interest in BATMAN BEGINS, and then said, ooh, he’s now starring in a movie called THE DARK KNIGHT? Is it set in the days of King Arthur? Does our hero speak with a British accent while on horseback with his trusty lance at the ready?
That’s what I was going to say. Although IIRC the sequel was released under the name Mad Max 2 in Australia and maybe other countries, but in the US it was titled The Road Warrior with no indication whatsoever that it was a sequel to Mad Max.