This makes a fair bit of sense. I can see why they'd want to expand the cast and mix character roles around a bit, during development.

If Selphie and Irvine were late additions to the plot, that might also help explain why they have relatively little to do, story-wise. Much like everyone else who isn't Rinoa or Squall.

That part about the shadow on the Dollet beach is a neat find, it's cool when the game leaves little clues/details like that which show how things developed. Even if it is technically an animation problem or an editing oversight.