You're asking that on the wrong laptime page, I'll answer anyway
All the manufacturers and most magazines test on that short version of the track (Autobild being the most notably exception, using only the full track), however, Porsche does not claim the lenght of the lap, but, since factory claims have been met on the full track and or reached fairly easy on the 20.6km one, is more than likely than Porsche claims are for the full track (IMHO).