Domains with multiple TLD entries don't show creation/expiration dates

[smith]

Doing a query with a domain like yahoo.com or google.com can give back a bunch of entries, like this:

YAHOO.COM.ZZZZZZ.MORE.INFO.AT.WWW.BEYONDWHOIS.COM
YAHOO.COM.ZZZZZ.GET.LAID.AT.WWW.SWINGINGCOMMUNITY.COM
YAHOO.COM.ZZZZZ.DOWNLOAD.MOVIE.ONLINE.ZML2.COM
YAHOO.COM.ZOMBIED.AND.HACKED.BY.WWW.WEB-HACK.COM
YAHOO.COM.VN
YAHOO.COM.VIRGINCHASSIS.COM
YAHOO.COM.TWIXTEARS.COM
YAHOO.COM.TW
YAHOO.COM.SG
YAHOO.COM.MX
YAHOO.COM.MORE.INFO.AT.WWW.BEYONDWHOIS.COM
YAHOO.COM.JTNELECTRIC.COM
YAHOO.COM.JENNINGSASSOCIATES.NET
YAHOO.COM.IS.N0T.AS.1337.AS.SEARCH.GULLI.COM
YAHOO.COM.HK
YAHOO.COM.ELPOV.COM
YAHOO.COM.EATINGFORJOY.NET
YAHOO.COM.DALLARIVA.COM
YAHOO.COM.CHRISIMAMURAPHOTOWORKS.COM
YAHOO.COM.BR
YAHOO.COM.BGPETERSON.COM
YAHOO.COM.AU
YAHOO.COM

When a domain gives entries like this, the creation and expiration dates can't be found. Is there a way to query only for YAHOO.COM and ignore the others?

Some whois servers tell you this:

To single out one record, look it up with "xxx", where xxx is one of the
of the records displayed above. If the records are the same, look them up
with "=xxx" to receive a full display for each record.

But I haven't been able to do this from the ruby client.