Fair enough, rn.
Here's the link I was looking for:
http://www.caa.govt.nz/fulltext/Fata...-HVN_Fatal.pdf
Crucial part is pages 7-9. Looks like it was a bit more subtle than just missing out the flexplate. Seems the bolts were assembled incorrectly, negating the effect of the flexplate, but from the look of the diagram this would be really difficult - if not impossible - to spot during the normal Check 'A'.