Hi Anaïs,
To differentiate the data system needs some identifier from the user group (subsidiaries), in SAP CRM business role concept (role config key ideally) does provide the same. So even if subsidiaries uses same functionality and follow same process still you can use business roles and achieve your requirement in a standard and simpler way.
Also if you take a broader view the business might ask for similar differentiation for other objects like transaction etc in future, in that case also business role will help you.
There is another access restriction feature in CRM called ACE but it won't be useful in your scenario as it works on object level but you are looking for access restriction within an object.
Regards,
Shobhit