How does ReqIF import handle: custom attributes with lists of values; or custom attributes from multiple sources?

Hi all,
If I import a ReqIF file into RRC, I've read and understood that any non-system-defined attributes will be recreated, even if I've already set them up in my project area:

Important: A ReqIF import creates types and artifacts during the first import into a project. Later imports of the same data update the existing resources, except for view column information. A ReqIF import only merges system-defined attributes and types. All other artifact types, attributes, data types, and folders are created in the project you are importing to if they have not been previously imported from a ReqIF file. For example, if you have a Priority attribute in the ReqIF file, and the current project already has a Priority attribute, the import creates another attribute that is named Priority2.

To work around this I've seen guidance that says I should consider importing ReqIF files to create any custom attributes. Understood.

Now, given all the above I'd love more detail on how these scenarios are handled:

1.  The external system (e.g. DOORS) has a custom attribute with an enumerated list of values. Will the full list of values be carried in the ReqIF file? If so, will RRC 4.0.x actually import that full list when it creates the new attribute? I guess another case to consider would be a system attribute that has been extended with additional values.

2. If there are two external systems (e.g. a DOORS system and another Jazz RRC instance) and my RRC instance and all three use a specific custom attribute (e.g. Special_Category) and I import ReqIF files from both external systems will I end up with Special_Category1 AND Special_Category2 or just Special_Category1?

I'm trying to plan out migration paths but I don't have a 4.0 system yet to test with.

Thanks,
Andrew