Medical records can be divided into four major components:
1. Medico-legal documents
2. Summary documents
3. Observation documents (lab reports/xray reports, etc.)
4. Process information (progress notes, procedure notes, etc.)
In the process notes, doctors not only note what they observe, but what they are considering, planning, and anticipate. These are working notes, or, in essence, notes to the doctor from himself regarding what's going on in the patient. They can include differential diagnoses, subtle observations, or "heads up" messages that help the doctor keep track of the patient without formally documenting it.
Two quick examples:
1. the patient is anxious and defensive. The differential might include drug abuse or mental illness, as well as social emotional stress (concern about interpersonal relationships, extramarital affair, etc). Recording "potential drug abuse" or "rule out schizophrenia" as a formal diagnosis would not be the kind of item a patient would be pleased to read in their record, or would necessarily want to be reported to their insurance carrier as part of medico-legal documentation. Alternatively, if mental illness is suspected but cannot be diagnosed, the doctor would want to note changes over time without making a definitive diagnosis. If the stress is induced by social emotional distress, it may well go away without ever being overtly documented or communicated.
2. A pediatrician notes that a child has several bruises. The differential includes normal active childhood, leukemia, and child abuse. A parent would be extraordinarily upset to see leukemia mentioned in a note. Likewise, for child abuse, if there's no abuse, the parent would be offended or insulted. However, if there is, then the parent might well change physicians, putting the child at risk for continued abuse.
Medicine, like the rest of life, is not simply black and white.