Hello again,
I've talked with the CS team, and have come to conclusion that you did complete the quest previously in 2020. There is a specific variable that is triggered when a player starts the battle with the quests Valentine Clefable, and we found that on your account. However, there is not a specific variable that shows if a player actually catches the Clefable. I have searched significantly and have been unable to find the Clefable either released, submitted to Collector Joro, or traded to another account. As far as I can tell, you battled the Clefable but failed to catch it.
I know this is probably not the answer you wish to hear, and I apologize that I am unable to provide you with a better one. However, you can still encounter Valentine Cleffa, Clefairy, and Clefable where ever they spawn in the wild, including on the Event Island at the spawn Aphrodia Island West.
Please let me know if you have any further questions