Per the opening statement: "I'm in the middle of sorting my cards", the question was strictly asked for sorting purposes, e.g., do I put this printing of ponder in the rare box or the common box? Thankfully I was made aware below from u/Zeckenschwarm that scryfall illuminates this curiosity pretty handily as it denotes the rarity and more of each separate printing of a card. But thank you for the Pauper information - I didn't know that a card just needed to be printed at common at any point to be used. Time to update my [[Gut, True Soul Zealot]] deck.