the holiday model for OSRS is basically you get all the rewards from previous holidays once you do a holiday event. So if you do the Halloween event that's currently going on and it's the first Halloween event you've done on OSRS, you get this year's rewards plus all the rewards for every Halloween event before.
I like the system if only because I'm a shallow motherfucker that just wants to go around wearing the yellow partyhat like a crown and the green one is nice to wear for farming runs.