After applying the latest monthly patch update on our CA API Gateway (CA_API_PlatformUpdate_64bit_v8.1-RHEL-2018-04-24, CA_API_PlatformUpdate_64bit_v9.X-CentOS-2018-04-24.L7P or later) running rpm on the machine will list more than one kernel version.
[root@server~]# rpm -qa | grep kernel
This deviates from previous behaviour when applying the monthly patch update. Typically we would expect to see only the latest kernel versions.
rpm as such will list all packages installed and/or available on the machine.
By keeping 2 versions of the kernel, we have the option to rollback, in case a kernel bug is found. This hasn't been done in the past, but has been added to the monthly patches.
So while the machine itself is running on the latest package listed, the previous package is still available on the machine, so that a rollback is still possible.