I think with an item like that, Rumple probably put some clause in the Curse that would keep it close to him, but hidden from him, so it couldn’t accidentally be found and/or opened.
I think that the key here is…well, the key. LOL. The door wouldn’t have activated unless he put the chipped cup in the little holder and we don’t know yet how Gold viewed the cup. For all we know, he thought it was just a random object in his shop for sale. (side note : I’d like a Mr. Gold flashback to the day he woke up and went to his shop and saw Bae’s toys and Belle’s cup. I think I need that badly)
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"He was a lot of things to me" "The only conclusion was love"