Timelines - the CVs have no idea what happened when. Durga was first created for Mahishashur, w/ the various deities (not Parvati) invoking her, giving her their shaktis and astra-shastras. The story of Shumbha happened later, when Durga was a part of Parvati. Oh, and one more thing - Kartikeya was one of those who gave Durga his shaktis in both stories, but as per this serial, he's not born as yet.
On the contrary I think they do know what happened when. Clearly they are deliberately making changes because they feel it's better that way, to spice up the storylines, add more asurs to Taraka's story to make it cooler and so on. Although why they didn't use the South Indian version I don't know; because that one has a zillion asurs already in the story. 😆