What’s the problem with having limited time “Had to be there” rewards?
Every collection game needs commons and rares. Limited time offers is just one type of rare. Special events should have special event rewards. Something that people can get for participating, a trophy for having been there and done the content.
Because someone has 2015 little league trophy from the Townville league championship and you think it looks better than your trophies doesn’t entitle you to it. It was the trophy for the 2015 Townville season. You had to be there to win it then.