The Scientific Linux release notes are considered additive. This means that the one set of release notes, is meant to be added to the set below it. So the Scientific Linux notes, are changes that Scientific Linux did to the vendor's release. And the vendors update release notes are the changes that they did to the release before it.
If we did not have a Scientific Linux release for an architecture, there is no corresponding Scientific Linux release notes.

Scientific Linux 3.0.8

i386
SL 3.0.8 Release Notes
Vendor Update 8 Release Notes

x86_64
SL 3.0.8 Release Notes
Vendor Update 8 Release Notes

ia64
Vendor Update 8 Release Notes

Scientific Linux 3.0.7

i386
SL 3.0.7 Release Notes
Vendor Update 6 Release Notes
Vendor Update 7 Release Notes

x86_64
SL 3.0.7 Release Notes
Vendor Update 6 Release Notes
Vendor Update 7 Release Notes

ia64
Vendor Update 6 Release Notes
Vendor Update 7 Release Notes

Scientific Linux 3.0.5

i386
SL 3.0.5 Release Notes
Vendor Update 5 Release Notes

x86_64
SL 3.0.5 Release Notes
Vendor Update 5 Release Notes

ia64
SL 3.0.5 Release Notes
Vendor Update 5 Release Notes

Scientific Linux 3.0.5

i386
SL 3.0.4 Release Notes
Vendor Update 4 Release Notes

x86_64
SL 3.0.4 Release Notes
Vendor Update 4 Release Notes

ia64
Vendor Update 4 Release Notes

Scientific Linux 3.0.3

i386
SL 3.0.3 Release Notes
Vendor Update 3 Release Notes

x86_64
SL 3.0.3 Release Notes
Vendor Update 3 Release Notes

ia64
Vendor Update 3 Release Notes

Scientific Linux 3.0.2

i386
SL 3.0.2 Release Notes
Vendor Update 2 Release Notes

x86_64
SL 3.0.2 Release Notes
Vendor Update 2 Release Notes

ia64
SL 3.0.2 Release Notes
Vendor Update 2 Release Notes

Scientific Linux 3.0.1

i386
SL 3.0.1 Release Notes
Vendor Update 1 Release Notes

Scientific Linux 3.0.0

i386
Vendor Release Notes

x86_64
Vendor Release Notes

Other Notes

README's
README-i386-en
README-x86_64-en
README-ia64-en