The Bluebook and prices at the online auction sites will give some idea.  A pre-war A-5 must be in near perfect condition to be worth much.  They usually have something broken or are just worn out.

The Bluebook also has serial numbering information to help figure out when the guns were made.

Post war guns bring stupid high prices, even dogs that show their time in the duck blind.  A rusty gun will still bring $350, and I mean one that isn't fit for a wall hanger.

Check the butt stock for cracks at the tang; nearly every gun has one unless the stock was changed and not shot much afterwards.