Universal Containers uses a Private sharing model on Accounts.

With Account organization-wide defaults set to Private, users cannot automatically see records owned by peers at the same role-hierarchy level. Salesforce sharing rules provide an exception to restrictive organization-wide defaults and can grant additional record access to selected users, roles, or public groups. If User A belongs to a public group targeted by an Account sharing rule, User A can receive access to User C ' s Account while User B does not. Being at the same role level as User C does not provide upward hierarchy access. “View All Fields” concerns field visibility and does not grant access to otherwise inaccessible records. Login access policies concern when or where users can authenticate, not access to one particular Account. Therefore, membership in a public group used by a sharing rule explains the different record visibility.

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