The 1989 catalogue of manuscripts in New Zealand was the first attempt to pull together what was known about the manuscript and list its dispersed leaves. As mentioned in the previous post, this was the first time that the manuscript was associated with John III of Ghistelles:
This passage cites two sources. First, E. Warlop, The Flemish Nobility Before 1300 (2 vols, Kortrijk, 1975-76), which reproduces the arms of various members of the Gistel/Ghistelles family, including John II:
Another medieval source, the Wapenboek Gelre, or Armorial de Gelre, now in the KB, Brussels, gives John III's arms quartered with those of Luxemburg (he had married Marguerite de Luxembourg in 1289):
The second article cited by the New Zealand catalogue (if I understand it correctly) says little specifically about John III's arms, but suggests it did not have the label of five points:
"Willem (1276-1297) van Gistel, een andere jongere broer van Jan II, had alleen een wapenzegel waarop een schild met een effen keper.
I'm not sure where all of this gets us, except to say that the sources are not very clear about which arms John III would have borne c.1300, when the so-called Ghistelles Hours was produced.De volgende generatie, namelijke Jan III (1289- +1315), heer van Gistel, en zijn jongere broers en zusters, gebruikte uitsluitend de keper van hermelijn, en van dan af bleef deze het wapenteken van het huis van Gistel." 
And it is worth mentioning that other heraldry occurs in the manuscript that is certainly not a variant of the normal Ghistelles arms: 
It is perhaps more fruitful to approach the problem from a different angle.
Of all the known leaves of the Ghistelles Hours, only one has the arms of Ghistelles and Flanders. They are not placed at a major textual division, as one might expect if they were intended to signal the identity of the patron of the manuscript. Typically, when the arms of a patron occur, they are placed at the beginning of a manuscript on the first page of the main text, and sometimes also at the beginning of other major textual divisions.
As it happens, the first leaf of the Hours of the Virgin of the Ghistelles Hours survives, and was sold by Christie's, 4 June 2003, lot 5:
In the next post I'll consider some possible alternative patronage of the manuscript, and suggest why the Ghistelles arms were included on one of its leaves.
 I am grateful to Dominique Vanwijnsberghe for obtaining for me a scan of this article, apparently not available in the UK.
 EDIT. As originally posted, I did not mention that the rampant lion is not facing towards our left, as is normal, but instead facing to our right. Right-facing lions can occur in real heraldry, but they are very rare, and it seems more likely that the artist has simply got it "wrong" -- further evidence that he is using heraldry for decorative effect, rather than to accurately identify the arms of the patron.