Existing Wording
managingOrganization - The organization that has assumed the specific responsibilities for the specified duration
period - The interval during which the managing organization assumes the defined responsibility

Comments
It would appear that managingOrganization and period are intended to be tightly coupled. I think it would make sense to incorporate them into the specification as tightly coupled items. E.g.\\managingOrganization
-> reference
-> period
It might also make sense to allow for multiple different managing organizations.

Grahame's Comments
makes sense to me