In Charles Clarke's book, "Nepenthes of Borneo", CC has dismissed the existence of N. maxima from Borneo but in the new photos posted on exoticaplants of Australia is a very beautiful pitcher of N. maxima claimed to have been collected in Sabah. The form "Pieriensis" can be viewed on:
If that is the case, the number of species in Borneo is increased by another one.
Charles knows about this example and says it is not true(I emailed once and asked). The most likely scenario is somebody collected seed from several major areas(Sumatra, Borneo) on one trip and mislabled the collection area.