U.S. Copyright Regulations Question

[Robert Cianchette <rmc -at- DAVIDGE -dot- COM>]

Greetings,

I'm wondering if a kind reader could provide me with some definitive copyright
information.  Specifically, I would like to know what the generally accepted
legal practice is for specifying copyright dates on continuously updated
publications (i.e. software and user manuals.)

I've seen examples such as "(c) 1987-1993" and "(c) 1987, 1989, 1993".
Should the copyright date reflect the years in which any new version/edition
of a work has been produced and distributed?  Is it not considered sufficient
to note the date for the current version, assuming that previous versions
also stated their appropriate date?  Is the idea that portions of the work
were published/copyrighted in these years, so it's wise to note all dates?

I'm not really interested in conjecture/opinion (I have more than enough
of my own, thanks!) as much as I am in getting a response from someone that
has first-hand familiarity with U.S. copyright regulations.  I realize that
I should consult an intellectual property attorney, but my boss is too
"frugal" to follow this approach.

Thanks for your time,

Robert Cianchette       rmc -at- davidge -dot- com