Accounts can only be assigned to a single parent organization and will not be available to other areas that have different parent orgs.
As illustrated by the attached org hierarchy chart, accounts can only be assigned to a single ParentOU at a time. As an example, Account C is not available for assignment to the 'Team 1.1.2' OU as the account has been assigned to the parent group 'Business Group 1' and 'Product 1.2'.