I looked into this a while ago. Unfortunately most of the pre contact sweet potato cultivars that were grown in NZ have been lost to time, as larger growing imports were adopted. There may be some original samples in a Japanese seed bank somewhere.

https://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&object... https://www.jstor.org/stable/4257220?seq=1