I have just finished Final Fantasy 1 and there are a lot parallels with Final Fantasy 9.
The crystals(the big one and the four smaller ones)
Garland and the things he says.
The Four Chaos Demons
The world looks roughly the same in both games(accept place locations in the game).
Most of the dungeons have the same names.
You have the Dwarfs that go 'Rally Ho'.
The stories can be linked together.
I am sure there are others...
Is it coincidence, the games are linked in story or Square really ran out of ideas come Final Fantasy 9.