Hi Susan,
Yeah... PMI is not doing a great job in explaining what's really going on here. There answer to you is lacking the full depth. For example what they completely omitted is the fact that while it's a good idea to read PMBOK 7 as you prep for the exam, many of the questions that focus on processes will use the 6th edition as the source.
As Harry has said, the PMBOK Guide is really only one of about 10 reference books for the PMP exam. And PMI is really clever here... they don't mention which version. They just say "The PMBOK Guide is a reference book". This allows them to use any version they want. But... did they tell you that? Of course not.
Additionally, PMI realized that the new version 7 is really not answering the need of many people. V7 talks a lot about principles and domains. But it doesn't offer any step-by-step help for projects. So they are now developing a "process guide", which is supposed to be published later this year. (My best guess, once that is out, then it will become a reference for the PMP exam as well).
So - unfortunately - the situation we find ourselves in right now is a bit murky. PMI isn't giving clear guidance and the best I can do is to recommend to "read across" both versions.
To close... our training course is fully updated to cover the material that is required for the exam. Because that material is clearly described in the ECO. (Again, Harry mentioned that).
