API has a guideline for almost every system of a compressor. NO compressor set is 100% compliant, as it is a set of recommended guidelines and not a hardened requirement.
The API sections that are the most followed, are those that set to guide the pressure housing design, rotor dynamic design, and process connection design, and perhaps shaft sealing design.
As the customer you can require that certain parts of the API guidelines be followed, or you can allow exceptions to the API guidelines, as you feel is adequate for your application.
You should get a copy of API 617 and go through it yourself, to see what it really discusses.