Adobe Stock photos licenses

We have a company that creates material for klients using Adobe stock images.
The klients then want access to the material to later on be able to create thing with the images.
The licenses of the images can be transfered in Adobe stock to that klient (company) but the text also states that a written agreement is needed?

Please note that a license can only belong to either you or your customer (not both), and that a license can only be transferred to a customer via a legally valid written agreement between you and the customer. Also, keep in mind that this action cannot be undone and that the status and information about the transfer (customer's name and additional notes) will be visible to all users in your organization.

I was just wondering if this really is needed, or will it be enough only using the licens "transfer" in Adobe stock? They already have a contract with the customer to create material for them. 

Thanks
Chris