Old saves at least as old as version 0.10 (since I don't have previous builds' saves) are retrocompatible, so there should be no issues on that regard.
As a reminder, PLEASE (and I can't stress this enough) check the guide here to check whether or not you have finished all the events available in the game/reached max level with everyone to be able to proceed with (hopefully) no issues.
Now, in the event of so many people having issues to activate the events added in this update, I decided to download the update to troubleshoot it with my save since there's a lot of people that seem to not have the events trigger properly even AFTER replaying the Halloween event (which you only need to activate again after completion and go directly to sleep, no need to redo all the scenes).
For whatever reason, my save works perfectly (at least with the Christmas one, since I just launched the game). I'll add it to this post for you to check out.
This save starts you at the attic right in front of the gifts required to activate the Christmas event.
I'm playing through all of them right now so I'm unsure if it won't cause an issue/not trigger the other events, so hang on until I test it fully.
EDIT 1: It works with the Mother's Day event with no issues. Checking whether or not it works with the last Event in a bit more.
EDIT 2: It works with the Easter Event too, so officially this savefile provided WORKS for the Holiday Update's events with no issues whatsoever so please feel free to use it.
As a final note...
PLEASE, FOR THE LOVE OF C̦̥̥͓̼̖̣̍̐̌͑̆͑͗͘͟͜͝T̼͉̹̥̠̃͗̾̈́̉̐ͅḦ̨̺̪̰̻̞̺͇́̊͑̇͆͗͞͞Ṷ͙̦͎̋͐̈̍Ḻ̮̼̤̏͗̍͠H̛̳̤̻͈̽͑̎Ü̹̪̆, READ THE GUIDE HERE TO BE ABLE TO TOGGLE SAID EVENTS AND STOP ASKING THE SAME QUESTIONS ON HOW TO GET THEM.