The 'Install Experiments' is a static utility which contains a list of the most up to date released content at the time that the version of LabAuthor was installed. The experiments are copied to the users computer at the time of installation, but are not installed (unless they are chosen to be installed).
Any content which has been released after the current LabAuthor version, will not be shown here until an update for LabAuthor is released/installed. This is the expected behavior for this utility.
The 'Check for Updates' is a dynamic utility which uses .plist files to get the latest experiment lists from the ADInstruments website. The experiments listed here will always be the most recent versions. Using "Check for Updates" will ensure you are installing, and seeing the latest content. When updates to LabAuthor become available, the 'Install Experiments' utility will have updated experiments to match the latest releases.