I noticed some small possible mistakes in the old HSK decks. The HSK 4 deck has only 599 words, not 600. Is one word missing? After a quick check I think the word 号码 might be missing.
Also, the first section in HSK 6 deck has 96 words and the last sections has 104 words. According to the names of the sections, both should have 100 words.
The HSK 2 deck has one extra word (the last section has 11 words, not 10). This is actually correct, because 虽然……但是 and 因为……所以 have been counted as two words (giving 2 extra words) and the two meanings of 对 are counted as one word (2-1=1). The description text “Our HSK 2 list covers 150 words. Our HSK 2 list covers 150 words” is a bit misleading (and written twice).
Sorry for nitpicking!