[exim] duplicate routing when using driver=accept

I have users in /etc/passwd user whose mail is routed using an "accept" router.

I have non /etc/passwd email accounts whose are routed using a "redirect" router
and .cdb files.

I have a few instances where user@password wants a duplicate email sent to user@cdb.
If the email first goes to user@cdb, a duplicate should go to user@passwd

I have an Exim .forward entry for user@passwd with -> unseen deliver user@cbd

and for the user@cdb I have an additional cdb file for unseen deliveries to user@passwd

the user@cdb always only gets one copy of the email because of the internal checks
within the redirect router (I presume).

However the user@passwd always gets two copies, because I think the accept router
has no such check for duplicate deliveries.

Would someone kindly offer a way to prevent duplicate deliveries within the accept router?

Thanks
Jim