The practices listed in CMMI are vague. For example in Configuration Management Process Area the first practice says "identify configuration items" . What if we identify certain CM items which are important according to organization, will appraiser say you didn't add this item in your CM list and fail us.
What if in some practices we don't see business value and we don't implement, would appraiser say strict "NO" and we fail.
The CMMI model consists of Process Areas, Goals, and Practices (as well as many other things). As a Lead Appraiser it is my duty to verify that every Goal (specific Goal or Generic Goal) within the targeted maturity level, has been "satisfied." There is no opportunity for you to declare a goal "out of scope," with the possible exception of those within Supplier Agreement Management." We also EXPECT to see that all of the practices are being performed, or we expect you to demonstrate an alternative practice. The practices are used to satisfy the goals.
The example work products under each practice give you some idea of the types of evidence we are looking for - but it is only an example list - there are many other possibilities.
We are looking for two pieces of evidence - one "Direct" and one "indirect" which could also be an "affirmation" or a verbal statement. Both pieces have to be there to you to succeed for each practice.