https://labels.wmflabs.org/stats/<wiki>/<campaign id> shows which users' contribution an active campaign is based on, but once the campaign is finished, this information seems to disappear. It should stay available in perpetuity, both for AI transparency and for practical considerations such as T223882#5197556.
E.g. https://labels.wmflabs.org/stats/huwiki/33 (compare with https://labels.wmflabs.org/campaigns/huwiki/33 which does work)
See