Here's what's "new" in the remake that wasn't in OG (but was stuff we already knew from the comp) A thread.

Aerith mentioning she tried to leave Midgar before. This is from Before Crisis. Added in the remake, never in OG. "new."

Project-G and Project-S are from CC. Never in OG. "new."

Kunsel. Never in OG. In CC. "new"

Kyrie and Leslie. Never in OG. In the novella "The Kids Are Alright" that takes place after OG. "new"

The trio in Wallmarket. Andrea, Madam M, and Chocobo Sam. Actually new. Added to replace the tedium in OG of getting Cloud different dresses, also added to get Aerith different quality dresses. Made Wallmaret more modern. Dress redesigns. "new"

Roche. Actually a new character because in OG the only soldiers we saw were Zack and Sephiroth. Saw Genesis and Angeal in CC. Added because OG only had 2 soldiers. Unlikely Shinra only had 2 Soldiers. 3rd class soldier added to explain "1st class" rank never explained in OG.

Tifa and Aerith have 3 dresses to pick from for Wallmarket. New.

Underground human testing lab discovered. Never in OG. "new" it's Deepground from DoC.

Zerith. "new" OG didn't have the compilation that fleshed out what their relationship actually was.

Zack's last stand from CC is shown in the remake. It's completely different in OG. Zack's death expanded in the remake because of the comp.

It's not a new story, it's "new" because it's not a 1 to 1 remake. They said it'd be different and changed, but that the main story is still there and that isn't changing. It's retelling the story of OG with the compilation in-tact. It's trying to make a coherent canon.