The met date on redeemed events is the date that you set your Switch on, meaning it can legally be any date that the Switch allows. The wondercard is where the real-time date will be since that is set server-side, but theoretically there is no issues to have the date set as today.
It will just look suspicious to others. If you somehow have a Galar Shiny Eternatus with a met date of November 22, 2025 and you suddenly start listing that you have the Shiny Eternatus on the real world date of November 22, 2025, and you've had no indication that you've had it before then, people will ask where you got it from. Remember, injecting wondercards is legal at best and shouldn't be claimed as legitimate when talking to others.