Off-topic, but I was unaware there were any sealed Spanish promos from the WotC era. I’ve heard from three different sources the Spanish Moltres/Articuno/Zapdos WotC Promos of the second Pokémon Movie were only handed out non-sealed in the cinemas. Were these Ancient Mews handed out differently in Spain (like part of a DVD or something)? Because the Ancient Mews were also part of the 2nd Movie handouts in most cinemas i.I.r.c. Bit weird that those are available sealed in Spain, but the legendary birds not…
EDIT: Cancel everything above. Two comments below this one it is stated they turned out to be Italian instead of Spanish.
On-topic: The Ancient Mews themselves are the same as the English ones, so grading shouldn’t be a problem at all. There are only four different Ancient Mew versions, three from Japan, one from the US/Australia/Europe (the one you have).
Greetz,
Quuador