فَإِذَا وُجِدَ كَذَلِكَ، ثُمَّ زَادَ بَعْدَ ذَلِكَ شَيْئًا لَيْسَ عِنْدَ أَصْحَابِهِ، قُبِلَتْ زِيَادَتُهُ
Translation: If he is found to be such, and then adds something that his fellow transmitters do not have, his addition is accepted.
This is acceptance founded on demonstrated precision. Al-Nawawī distinguishes the addition of an accurate trustworthy transmitter from a rejected anomalous contradiction. The particular chains, substantive content, and stronger opposing evidence still require examination; not every conceivable addition is approved automatically.