About a month ago I did an upgrade of glibc on one of our test centos5 systems. And yum happily gave me about 8 packages, including both bitted-nesses of glibc-common.
This morning I was showing a co-worker how to upgrade glibc. And he found that yum wouldn't give him glibc-common-2.5-123.el5_11.1.i386.rpm.
So I browsed to the web interface of one of the centos5 mirrors, and couldn't find it either. Not in the x86_64 tree anyway.
Did that package disappear on purpose?