What is the reliability of a biopsy taken during a colposcopy?

This question can be rephrased. Can a biopsy not show the problem?

A colposcopic biopsy is reliable, on condition that it is taken from the right location.

There is the human subjective factor, which has partly to do with the doctor’s experience. There are, however, limits, because only the surface of the epithelium is examined during a colposcopy.

The doctor knows their limits and the limits of the examination, and will give you the right advice.