Currently the only event-label relationship is "presented by". But often, other players are involved in some way or another to the organisation of an event, in a way "presented by" would be anything but accurate.

An additional event-label relationship that is more open in nature.

My proposal would be to add something like "in collaboration with"

An example of "in collaboration with": https://musicbrainz.org/event/68e5abca-9837-4935-a1c3-55496166916b

(in samenwerking met is Dutch for in collaboration with). The one "presenting" is actually De Nor (currently only present as location).

In collaboration with can also be used for various prominent mentions of label/company/organisations involved in an event, but not actually "presenting" the event. Not just for when it is literally mentioned as such. It's not uncommon all kind of organisations are mentioned in relation to a specific event, especially bigger ones.