If you are a Windows Insider looking for a complete list of what Preview Build is in which Insider ring, the Flight Hub is your go-to place.
It’s a dashboard Microsoft provided to quickly identify the latest Windows Insider Preview releases for PC, Server, and IoT. You can also look up the status of the SDK and ISO images. Each dates stated in the list also has a link that takes you to the release announcement or download page.
You can also check out the Windows Insider Program documentation including a complete list of new features and updates that have gone out as part of Insider flights for the current development cycle (which currently is 19H1).
Stay Insider and happy previewing.