Biscuits: Like crisps, biscuits are also highly processed and thus can be consumed long after their sell-by date. If they taste soft or soggy simply pop them in the oven to get them crunchy again. These can be eaten two months after the best by date.
If you should keep them around longer, they will go stale, just like bread, and they will begin to get moldy. If you see mold on the biscuits, it's definitely time to throw them away.
So far, Lucy has obtained 10 Gold Keys and 5 Silver Keys, a considerable amount of Keys for a single Celestial Spirit Mage. Lucy's ability to summon her Spirits is limited by how much Magic Power she has to sustain them, the more Spirits she summons and the more powerful they are, the more Magic Power she exhausts.
Lucy's mother did have all 12 at one point in time, but she didn't keep them. She passed Aquarius down to her loyal friend, before her friend gave the key back to Layla and the Layla gave Aquarius to Lucy. The only reason Lucy has most of the keys she does is by pure luck (i.e. Hiro Mashima).
During the 'Alvarez Empire' arc, Aquarius made a special return when she saved Lucy from Brandish. The summon got special permission from the Spirit King to help Lucy, and Aquarius left once more with a promise left behind. The mermaid told Lucy she has a new key that could be hiding on any continent nowadays.