Very simply. The right to sell "exclusive usage" in a license is only ONE right. That one can no longer be managed but there are plenty of other rights that can be assigned.
What do you call Alamy's L license? It does not offer exclusive usage. It just prices (manages) the license according to type and duration of use. It is
partially rights managed (just the same as the micros partially manage their libraries)
The buyer of an L license knows nothing about where or how that photo is being used, so why does the agency need to manage the history? It doesn't even try. When it makes a sale it doesn't contact you to ensure that the image is not for sale on another RM site, as it would have to do with a managed history image. I'm not sure but I think Getty's "rights ready" concept is similar: buy for a specified use but no guarantee of exclusive usage.
Fully RM images should be exclusive to one agent.
if an image of history can not be managed, how can it be 'rights-managed'?
I am sure there are buyers who will pay whatever, and don't care about RM or RF or don't even know what is that.. but as an agency, they should keep a previously sold RF selling as RM as long as the seller is honest.
For the 55,000 time, there is nothing that stops you from licensing previously sold RF images as RM. It only restricts you from offering image history or exclusivity as value added offerings. Sheesh.
I dont know if they still do but Alamy used to ask you notify them of rm sales elsewhere for non excl. files