Complete precision denotes exceptionally dependable preservation and transmission. Somewhat lighter precision retains an acceptable ability to preserve reports but falls short of that higher standard. Integrity and case-by-case verification remain essential in both categories.
Imagine two trustworthy pupils reporting from the same teacher. The first consistently matches other accomplished pupils, with very rare mistakes. The second makes somewhat more occasional errors but is not a habitually inaccurate transmitter. The first may approach the sahih standard; the second may approach the hasan standard.
Important qualification: a general classification of a narrator does not settle every individual report. A demonstrated error, stronger conflicting report, or hidden defect can alter the judgment.