Nowadays, ETBs are printed in massive quantities, but this wasn't the case in the Sun & Moon era, when ETBs weren't in high demand
The idea is that when a card is described as Mint then it is assumed that it is perfectly preserved, however it may have a few very minor printing imperfections such as being imperfectly centered or the horizontal lines that sometimes appear on Unlimited Edition cards
This seems like a fun Gruul Voltron Commander but is much less interesting than the previous two cards
For Shining Gyarados, that means that its card number 65 of 64
I think the reprint risk is pretty low, because how do you find a place where you can print a card with phasing again
Blissey has consistently appeared across generations, maintaining its position as a beloved support Pokmon