It does seem that 21CFR11 is mostly up to interpretation, and a LOT of standards like this are vague on purpose. What that purpose is I have no idea.
We usually go over with our customers what their specific requirements are for 21CFR11 (or any other standard). If you promise to build something that will get FDA approval, I think it is a mistake. If we promise to meet the customer’s specs, our job is very well defined and removes a lot of liability.
(also: resurrecting an ancient thread 
)