Look at these Wikipedia articles:
http://en.wikipedia.org/wiki/Red_Hat_Linux#Version_history
http://en.wikipedia.org/wiki/Red_Hat_Enterprise_Linux#Version_history
http://en.wikipedia.org/wiki/Fedora_(operating_system)#Releases
As you might see in these articles you should split the name differently:
Nahant Update 5 means: Nahant (nickname op Version 4) Update 5 (the 5th
update)
The article
http://en.wikipedia.org/wiki/Red_Hat_Enterprise_Linux#Version_history
tells you which kernel release is put on the DVD or the CD-set of the
RHEL Update.
Kind regards,
Jan Gerrit Kootstra