Looks like your limestone was tasked for hauling/construction/etc. When you examined the stones themselves, there was no stockpile designated under them. If you have other stone stockpiles in the fortress, they may have already claimed them. Or you may have accidentally designated them for use in another construction elsewhere.
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Movie details:
Movie Name: Division of labour in the construction industry
Submitted by: The Dark Bunny - 2011-09-25
Looks like your limestone was tasked for hauling/construction/etc. When you examined the stones themselves, there was no stockpile designated under them. If you have other stone stockpiles in the fortress, they may have already claimed them. Or you may have accidentally designated them for use in another construction elsewhere.