I have just tried to update to 4.9 a system that was installed from a 4.8 local repo. Because 4.9 has been moved to vault, as described by Johnny in http://www.linux-archive.org/centos/638644-centos4-rhel4-upstream-effective-..., the mirrorlist file basically contains invalid information.
http://mirrorlist.centos.org/?release=4.9&arch=i386&repo=os
To avoid the faff of having to edit the CentOS-Base.repo file, is there any reason that the mirrorlist files couldn't be updated to point to the available mirrors of vault.centos.org? It would make things SO much easier!
Cheers Tony