"There is no data available concerning the original length of plesiosaur IVDs."

As noted in Taylor and Wedel (2013:7-8), the unpublished MSc thesis of Mark Evans (1993) æestimated that the thickness of intercervical cartilage amounted to 14% of centrum length in Muraenosaurus Seeley, 1874 and 20% in Cryptoclidus Seeley, 1892."

Were you aware of this claim? If so, I'd be interested in why you considered it incorrect, and went with the much thinner 2mm of cartilage you used here.