What's the difference between School Data Sync (Plan 1) and School Data Sync (Plan 2)?

https://docs.microsoft.com/en-us/schooldatasync/create-users-for-k12-and-hed#prerequisites-for-sds mentions among the "perquisites to enable SDS for user creation" are School Data Sync (Plan 1) or School Data Sync (Plan 2).

Microsoft Partners have access to documents that explain Office 365 Education Plan A1 includes School Data Sync (Plan 1) while both Microsoft 365 and Office 365 Education Plan A3 and A5 include School Data Sync (Plan 2).

However, I can't find any details about the differences between the SDS plans on:

• https://www.microsoft.com/en-us/microsoft-365/academic/compare-office-365-education-plans
• https://docs.microsoft.com/en-us/office365/servicedescriptions/office-365-platform-service-description/office-365-education, which doesn't even mention SDS
• https://docs.microsoft.com/en-us/office365/servicedescriptions/office-365-platform-service-description/microsoft-365-education
• https://www.microsoft.com/en-us/education/buy-license/microsoft365/
• [EDIT] https://www.microsoft.com/en-gb/licensing/product-licensing/microsoft-365-enterprise?activetab=m365-enterprise:primaryr7 mentions "School Data Sync Plan 2 (plan details can be found https://docs.microsoft.com/en-us/schooldatasync/)" - but there are no details about the plan there

Does anyone know what the distinction is between School Data Sync (Plan 1) and School Data Sync (Plan 2)?