How do you find where 'attribute data types' and 'link types' are used in a DOORS Next Project?

I thought it would be a good idea to import an existing Project from DOORS 9.4 to seed a training project we are developing in Next. However, what actually happened was that on import into Next, it automatically created many attribute data types, attribute types, and artifact types that were duplicates. For example, the Project I imported contained 10 modules, each containing an object attribute called "Context." Once imported into NG, I discovered it had created a separate and uniquely named "Context" attribute data type for each module like this:
Context -- the first module in the list had this attribute data type created
Context 2 - the second module in the list had this attribute data type
Context 3 - the third module in the list had this attribute data type created
...
Context 10 - the tenth module in the list had this attribute data type created

There was also a corresponding artifact attribute created for each attribute data type in each module.
An artifact type was created for each module that was imported.

I cleaned up the import by, for instance, having the 2-10th modules all refer to the 'Context' attribute, to the 'Context' artifact type, and creating a single type of module, called "Requirements" and changing the artifact type of all the imported modules to "Requirements."

I *think* that I am not referencing any of the duplicate attribute data types, artifact attributes, and artifact types, and yet when I try to clean them up by deleting them, Next won't let me. For instance, it says that attribute data type that I am trying to delete is in use. This is the error message I get:

So that comes to my questions:
1) Is there a way to export to REQIF or import to Next such that creation of duplicate types is avoided? For example, how do I get Next to understand that an attribute data type named "Context" in module 1 is the same as attribute data type named "Context" in modules 2 through N, and it should therefore create a single "Context" attribute data type and not 10 uniquely named ones?
2) Now that I have gotten myself into this mess, how can I delete the duplicate types in the Project I imported? Currently Next won't let me because it claims they are in use. Manually, I can't find any uses of the types I am trying to delete, but I can't be sure there aren't any lurking in the database out of my sight. And I don't see a search facility in Next that would allow me to find uses of types so that I can de-reference/eliminate them and then perform the deletes.