Early specialists such as `Abd al-Rahman ibn Mahdi, Yahya al-Qattan, Yahya ibn Ma`in, `Ali ibn al-Madini, al-Bukhari, Abu Zur`ah, Abu Hatim, al-Nasa'i, and al-Daraqutni compared competing accounts by examining the grounds for preference.
A narrator might be generally trustworthy yet mistaken in one particular report. In another report the same narrator might preserve a unique but accurate detail. Hadith criticism therefore proceeds beyond a static list of narrator labels to close study of the particular transmission.
A critic's classification of a narrator as trustworthy is not an unconditional endorsement of every extra word or chain link narrated by that person.