The Mexican Postal authority, beginning in August 1856, determined that some control was necessary to thwart the robbery of stamp inventories being delivered to the remote offices from Mexico City. The technique employed, to render this control, was the implementation of a procedure requiring that the offices imprint the district name on the face of every stamp to make it "valid" for use. It was the plan that unoverprinted stamps were considered  valueless and unusable for franking letters. However, there are many occasions where stamps without district names were placed into the mail, generally because an office did not have an overprinting device; or the office had misplaced their device.