What a wonderful gift.

The dates in the picture are patent dates. All a patent date can tell you about an individual gun it that it was made "after that date".
If want to look them up http://www.google.com/patents

You might also want to check out the Parker site:
http://www.parkergun.org/

Chuck Hawks has a table showing the grades of various classic American shotguns and how they compare, more or less.
http://www.chuckhawks.com/shotgun_grade_chart.htm

Pete