I doubt that Stern will get stuck with ACDC. Reading other forums, there are lots of firm orders still waiting for delivery in USA and it sounds like it is more popular there now than during early release.
Just finished watching "ACDC Live at River Plate", how good is that!
All 12 songs on Stern pinball are played out of a total of 19 songs. Judging by the popularity of the boys in Argentina, any pinnies that Stern have left over can be easily sold to the South American public.