After reading this thread https://euw.leagueoflegends.com/en/news/game-updates/features/prestige-updates
I think that the 2019 skins should all became available at the end of the year, it only makes sense since they were released this year...better to bring them back at the end of the year than later on...or never.
If you are afraid people will complain they worked hard for the event skins then put then on the 2000 or 2200 points system, people would buy the pass and grind for a last change at getting the 2019 event prestige skins. And only then make then enter the vault, some people weren't playing when they came out, or were busy on that time of the year, I think this solution would make everyone pleased.
I know they are limited time, but its still 2019 they were released this year, so I don't think that's breaking your word.
Some really special skins came back even though they were limited, so what's the difference here?
Even the little ahri star guardian merch I bought in a hurry cause it was limited came back. Feels unfair the event prestige skins from 2019 won't get another chance. I understand they can't cost 100 points, just make them worth totens like before.