The pdftopdf does a wide range of page management options (multiple copies, N-up, page-ranges, page-set, ...) but modern IPP printers do many of the page management, too. This often leads to cases where an option supplied to the job is applied twice, for example instead of the requested n copies one gets n*n copies.
What is needed is that pdftopdf gets somehow informed about which options the printer already supports and therefore should not get applied by pdftopdf. As pdftopdf cannot IPP-query the printer to check by itself (it even does not know whether the printer is an IPP printer) and as the printer's capabilities do not change, the probably best way is to use the PPD file.
So the PPD generator for auto generation of the PPDs for driverless printing should put hints into the PPD about which options the printer already takes care of internally, so that pdftopdf can skip these options.
The options handles by pdftopdf are the following:

• copies
• print-scaling/fitplot/fit-to-page
• orientation-requested/landscape
• number-up
• number-up-layout
• page-border
• page-delivery/output-order/OutputOrder
• page-label
• page-set (even/odd)
• page-ranges
• mirror/MirrorPrint
• booklet
• booklet-signature
• position
• collate/Collate
• scaling
• natural-scaling

AFAIK Copies and OutputOrder are already handled. Am I correct that I should let pdftopdf only generate copies if the PPD has the entry *cupsManualCopies: True?
So for the other options we would need entries in the generated PPD, telling which options pdftopdf should skip.
In addition, there should be an entry added to the PPD, telling that the printer is an IPP driverless printer, so that options which are done by all IPP printers do not need to get mentioned individually.
Once we have this facility in the PPD generator I can add appropriate support to pdftopdf.