Hammad ibn Zayd was considered trustworthy and precise, yet his report differed in an important chain detail: he omitted Ibn `Abbas, while other strong transmissions retained the link. Several corroborating routes favored the connected version.
The judgment did not declare Hammad's entire hadith corpus unreliable. It identified Ibn `Uyaynah's version as mahfuz in this one comparison. General narrator accreditation and evaluation of a specific discrepancy were kept separate.
This demonstrates why a normally accepted narrator can transmit an inferior conflicting version. One can identify an individual lapse without alleging dishonesty or rejecting all reports from that narrator.