Zoho CRM--making invoices private

Zoho CRM--making invoices private

I have an "advertising representative" role set up with standard access. I just switched invoices over to private from Read/Write/Delete in Permissions but it doesn't seem to make existing invoices private--anyone within the advertising role can see the other reps invoices. Is this a glitch or am I doing something wrong? Do preexisting invoices not become private?