CUPS should not create temporary queues if there is already a permanet queue for the printer

[tillkamppeter]

If there is a printer in the network which does driverless IPP printing (or a remote CUPS queue) CUPS creates a temporary print queue when one tries to access the printer (the printers listed by lpstat -e and not by lpstat -v).
This also happens if for the printer there is already a queue set up manually, with ipp, dnssd, socket, ... backend. In this case the temporary queue could confuse the user.
If CUPS discovers an IPP printer, before listing it internally as a candidate for a temporary queue, it could determine its IP, host name, and IPP service name, and check these against the URIs of the existing permanent queues and skip it if the printer is already served with one of the permanent queues.

[michaelrsweet]

If we see a printer already configured with the same device URI, then we use the permanent queue.

For any other usage, it is impossible to reliably determine whether a printer is a duplicate.