The latest manual is on the Diamond website:
Diamond Aircraft :: Technical Publications The DA42 TDI manual states that it is an FAA approved document, but I couldn't find a number for V SSE in it. As I'm sure you know, V MCA is 68 kt and V YSE is 82 kt, I guess you'll have to determine the SSE limit between those for yourself. The FTO where I revalidate my MEP has a V SSE published in their own procedures and they selected 82 kt for this.
(Not an operator, but I've been digging through these manuals myself recently.)