Martin,
It cannot hurt to document what we know and to document any educated guesses we might have.
This has a couple of benefits IMO. One, it helps avoid, at some future time, redoing the analysis that's already been done. Two, it might get someone sufficiently curious to investigate further.
There's really no tricks required to get additional information. Quality time spent with a debugger or a disassembler will eventually provide all the answers you might like to have.
Whether or not this will be time well spent is for the person doing the work to decide.
The GPI Guide and Reference provides a lot of hints and to what GpiAbortPath does. Take a look at the sample code for GpiBeginPath. Given what we can see, I would expect GpiAbortPath to take a single HPS argument, as does GpiEndPath. I would also expect GpiAbortPath to release the resources allocated by GpiBeginPath and the other path building functions. See the GpiBeginPath Remarks panel for some discussion on how this all fits together.
The ddk sources have real world examples of these path APIs in the testtool sources.