[hnbad]

I think you misread that. America/Nuuk doesn't have reverse DST (which is easily solved by just switching DST and non-DST around). It starts DST at a negative offset because the offset is defined as relative to the previous day.

[LysPJ]

Yes, this is indeed a different situation and my comment doesn't make that clear. Thank for pointing that out. I've made an edit.