Well that depends on your perspective ( point of view ) of the title.

IV is literally showcasing the SNES power at it's finest/lowest. Meaning it is pushing the SNES to the limit. The problem with this game is the ( what I am calling ) hard-to-rock or pixel appearance of the characters on screen, in comparison to X.

Castlevania X : Vampire Kiss ( whatever ) is literally the SNES variant ( port ) of the PC-Engine game. What many companies did and still do today is just make an entirely new game with a new story. The reason why many people including myself champions this game is because of the PCE engine character being used ( who is also a playable character in Switch Smash Bros ). He appeared in more then three games and was the apex of the 2d Castlevania series. If you also did not know this Hudson Soft refused to part with the PC-Engine port of Vampire Kiss, as they owned partial-rights to the game. This is why it was never ported to the PSX and only the PSP until Hudson ( sadly RED as well ) properties was purchased and dissloved into Konami.

Falcom Y's did it with Y's IV on the SNES ( which is a joke compared to the PCE ).
"Hunter the Reckoning" had multiple sequels that was different games.
SNES and Genesis had the same SF2 game with network-play but both was limited.
( Note Turbo/Rainbow was only on the SNES, whle II was on the PCE ).