Could've made the Enterprise refit a retcon

The in story explanation why the Enterprise looks different having spent 18 months being redesigned and refitted creates the issue whether the refit is the same ship as TOS, if everything has been redone what's left? the frame? We can assume the ship's original skeleton is still intact but is it enough to consider the refit the same ship as TOS? They could've easily made it a retcon meaning no in story reason to why the Enterprise looks different other than the producers had more money and wanted to redesign everything so it would look nice in the big screen and the characters don't notice the difference, to them it's always looked this way, the change in appearance of the Klingons from TOS to TMP was a retcon until DS9 and ENT.

The Enterprise looks different when it shows up in Discovery that's a retcon as it retcons all TOS aesthetic which is unusual for Star Trek because past changes always give in story explanations to why things look different which sometimes can be nonsensical and drive you out of the story.