Birdie,
     I suspect the reason for two bibliographic records is largely a
matter of practicality in shelving.  Having a new bibliographic record
and classification number avoids the problem of mixing up the two titles.
How else would you handle two volume 3's, for instance?
Ann
_______________________________________________________________________
/ Ann Ercelawn                       /            Bitnet:             /
/ Cataloging                         /       ERCELAA@VUCTRVAX         /
/ Resource Services, GLB             /           Internet:            /
/ Vanderbilt University              /  ercelaa@ctrvax.Vanderbilt.Edu /
/ Nashville, TN 37240                /      Phone: (615) 322-3504     /
-----------------------------------------------------------------------