[V8i .NET C#] How do I delete a dwg xref that is not found? I don't even see the missing attachment like I do when dealing with missing dgn references

I'm trying to clean up missing dgn & dwg references for projects (either delete or reattach). I have everything working for dgn files but when I process dwg files I can iterate through the model & layout spaces (they appear a modelreferences) then parse the attachments in the models missing attachments do show up at all. In a dgn file I use Attachment.IsMissingFile or Attachment.IsMissingModel to determine if the attachment is missing.