looks like its only a soft retcon (on that part), as New Vegas does also hint that the NCR is on the verge of collapse, and they do still reference New Vegas and its Events, even House shows up.
Shady Sands falling in 2277 seems to be a reason why the NCR was so weak during 2281, and it seems the nuke was after 2281/Second Battle of Hoover Dam. 2277 was Shady Sands no longer being the Capital of the NCR.
Seems like Independent Vegas is the canon ending since the strip still exists and is shown.
But yeah its not gonna be a good or super faithful show it seems