(It just underlines how blinkered the TVA and He Who Remains were in their insistence on allowing only a single "Sacred Timeline" to exist. Seems to me they picked the wrong one.)
I think the only reason that particular timeline was considered "sacred" by Kang/He Who Remains was because it was "his" timeline, the one that he originated from.
I did wonder about the year for a few minutes because if he had Hela's headdress, my first thought was that was it would place it after Thor Ragnarok. But, if The Collector killed Odin at the same time he acquired Mjolner, that would have facilitated Hela's release.