RHEL Packages moving between fastrack and core distro
A while back, Red Hat started pushing out early-releases for some updates. I'm guessing it was due to customers and users asking for eary access to trivial fix's. These early releases were put into a repository ( channel for you RHN users! ) called fastrack, with the condition being that these packages had not been through the complete or proper QA process. Users were advised at the time they should be selective in picking packages from this repo, only to solve immediate issue and consider these packages to not really be 'recommended' by Red Hat. So, thats the background to the 'fastrack' entity.
These packages were pushed out at various intervals during the life of a point release, and then either rolled in or discarded completely when the next point release came around. Eg. Package-1.1-3 released into fastrack during the life of RHEL-5.2 might make it into the main distro when 5.3 is released. On the other hand, its also possible that by the time 5.3 came around this Package-1.1-3 had been updated to Package-1.1-4, making the Package-1.1-3 redundant ( unless one was on the EUS or the z-stream etc platform, but lets not get sidetracked here ).
That nicely brings me to the point of considering update and upgrade notifications. Red Hat publish release info at various places, and there are different mechanisms for one to get to those notifications. One can get them via email, on the web, within RHN, through oval notifications in some cases etc. But the interesting point is - announcements are not re-issued when packages from fastrack move into the main distro. There is a nice silent move from one to the other. So if you are not tracking announcements within the fastrack repo, you might see something sneak up on you that has no origin notification issued ( or so it would seem to you ).
Within CentOS we dont have this issue. Mainly since we don't build the fastrack rpms regularly. There are quite a few reasons for that, I'll blog about why we did'nt and how we are going to try and solve that problem with 5.6 and 6.0 going forward. But the main thing is that we dont build those fastrack rpms at this time and have'nt done so in the past. Which creates an semi-significant difference in the announcement stream, in that we will announce those packages which have moved from fastrack to the main distro - but we will announce them when they hit the distro. But there will be no announcements within CentOS for packages that are released upstream into fastrack and then never make it into the main distro. I havent done any work to quantify this, but there are examples of when this has happened in the past.
So, if you are going to compare announcements. Keep this one thing in mind. Also, to all the people scraping the centos-announce mailing list to get update details into your automation, please consider using an alternative route. There are quite a few other options, use one of these alternatives.