I also understood that there had been one test well drilled in ANWR, but that the findings were not public.

I did a fairly intensive search of the EIA, though, and could not find any reference to the test well. Instead estimates of oil resources seemed to be based on comparisions of other areas with similar geographical structures.

Does anyone have any more solid data on what we actually know about potential resources in ANWR?

the 10 gb figure is apparently the mid range of usgs estimates, based on very limited information, making lots of assumptions and applying monte carlo simulation.
when i first started learning fortran* the prof had a saying "gigo" (garbage in garbage out)

* that was back in the days when programing was done on punch cards (shortly after we graduated from basic programing - the programs were saved on tickertape)