Some stories for the holiday events, like the last years Lunar Revel one, can easily be tied into the Mythos of Ionia (due to it being narrated as a holiday story). Also there is nothing stopping people celebrating the Harrowing, despite the actual Harrowing being this horrible cloud of nightmareish doom that can be cast upon you at any moment during the year (its like if a lot of people celebrate something without knowing the actual origins and threat of the real deal). Same can be said about Time of Snowdown, while not every year would be precieved as the canonical in lore celebration of the event, there also isnt much against the option of the holidays existing in lore, in some shape and form.
For now, for better and worse, you can interprate the events as canon or not in any way you want instead of people here telling you cant.