This post is not specific to Seamly however it may be of interest to some.
This paper was presented at this years Siggraph (2018) Vancouver Canada.
Warning… This paper is math based
Huamin Wang. 2018. Rule-Free Sewing Pattern Adjustment with Precision and Efficiency. ACM Transactions on Graphics (SIGGRAPH), vol. 37, no. 4, pp. 53:1–53:13. Link below