This is the last thing I have left to fix to pass the pre upgrade check. There are a three features that are referenced by the content but not installed on the server (not sure how this happened). Two are unnamed and one has an invalid scope.

My question is, how do I go about removing these features?

Here is the output from the preupgrade check:

* Name = IPCSmallSearchBox, Feature id = 2636a3cf-91e0-4e72-af0e-41c157d3c98a, Reference count = 1, Scope = ScopeInvalid, Status = Missing
* Name = Unknown, Feature id = 78b94e15-23ce-43f9-8036-babd847497d1, Reference count = 2, Scope = Web, Status = Missing
* Name = Unknown, Feature id = b350420a-9b03-4e21-bc70-359e84f65359, Reference count = 3, Scope = Web, Status = Missing

Specifically id like to know how what scope=scopeinvalid means. Is it, the feature was scoped at the site level, activated then changed to web level and then goes missing?