Haven't found any way to access standings of contest which belongs to a group, even when anybody can see them (e.g. https://codeforces.com/group/a7fj9QBnKu/contest/333884/standings).

UPD1: I tried to find the contest in 'contest.list', but it doesn't show there, even with my API key. As well, I tried to add parameter 'group'/'groupId' in link, but that doesn't work too.