-they stored
The word almacenasen is the imperfect subjunctive form of almacenar in the third person plural.
See the full almacenar conjugation


Ello no obliga a imponer una prohibición total de esos materiales, pero se podría instar a los Estados a que impidiesen que las personas y entidades incluidas en la Lista los obtuviesen, controlasen, almacenasen, empleasen o procurasen conseguirlos.
This need not require a total ban on such materials, but States could be urged to prevent listed persons and entities from obtaining, handling, storing, using or seeking access to them.
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