That's not quite true
@RenJones.
As an MCT you can only teach Microsoft Official Courses your technical certification is aligned to. Details of what technical accreditation is required to teach each course is included in the Courseware Title Plan and MCT Competency Requirements which is linked from MCT Central in the blue box. Learning Partners also have access to this spreadsheet.
However if the course is NOT listed on the sheet (community or custom course) then you can teach as you are confident to do so.
Personally I feel that if you have enough knowledge to teach an official course then you have enough knowledge to pass the exam which is stated as the requirement to do so and if you can't pass the exam you are not knowledgeable to be teaching it.