Almost every ebay seller who finds one of these dates (1880, 1887, 1912) on a cigar box claims it as the date of the box. Sadly, those dates have little or nothing to do with the date of a box.
 1880 is found on nearly all CigarMaker's Union stamps. The date commemorates the first Union stamp and is found on all Cigar Maker's Union stamps issued between 1888 and 1974. It is NOT the date of your box.
 1887 is found on the bottom of lots of Florida boxes. The date commemorates the founding of the city of Tampa and is found on all Tampa boxes from 1910 to the 1960's. It is NOT the date of your box.
 July 16, 1912 is found on all green Cuban Guarantee stamps. The date commemorates the issuance of the first government guarantee on that date in 1912 and appears on ALL Cuban cigar boxes exported between 1912 and today. If your warranty stamp has any English, German or French text it dates after 1924. There are other ways to tell if it's after 1960's.
 If a box has a small notice which begins :"The cigars herein contained were manufactured to retail..." it dates after 1919.