Parker produced a very wide range of boxes for the Parker "51", for both single pens and sets.  Some are basic cardboard boxes, but some were quite luxurious, such as the leather covered box for the early Parker "51" Presidentials.  Most Parker boxes are numbered, but they are never dated.  Nevertheless, by looking at ads of the era and New Old Stock sets found with instruction brochures and/or pens, one can come very close with the years in which they were used and the appropriate pens/sets for each.  In addition to the traditional clamshell boxes, most also included an outter cardboard box or sleeve to protect the actual box.  Prices of boxes are generally in the $10-$20 range, but can go over $100 for the rarer ones.  Condition is essential in collecting boxes and the biggest challenge is probably finding a clean inside, as most suffer from pencil marks and/or ink stains and the lining is nearly impossible to clean.  The outside is usually sturdier, but can get very soiled.  Cardboard boxes do not stand up well to wear and are often ripped or badly dog-eared.