With respect, everyone who has said that you don't get SB and ShB access until EW official release (Tuesday 07 Dec) is wrong. In the past, people who preordered an expansion have always been granted previous expansion access as soon as the new expansion's early access period began. If someone has Starter Edition now, and they preorder Endwalker, they will get access to Stormblood and Shadowbringers at Endwalker early access, Friday 03 Dec.
Here is a snippet from the
Stormblood Early Access Details announcement: