Within Azure's portal, The deployments page for a resource group lists deployments with a unique name. If a deployment is created with the same name, it appears to overwrite the previous deployment, to the extent the previous deployment is no longer visible within the deployment list. There appears to be no filters or groupings that can be unset to allow viewing a list of all deployments that have occurred.
How can I view a list of all deployments within a resource group, independent of their name?