Classifying an additional narrator as mazīd fī muttaṣil al-asānīd requires important conditions. There must be reliable explicit evidence of direct hearing at the very point where the additional transmitter occurs, and the version omitting him must be better preserved than the version adding him.
«وَشَرْطُهُ أَنْ يَقَعَ التَّصْرِيحُ بِالسَّمَاعِ فِي مَوْضِعِ الزِّيَادَةِ»
A condition is explicit evidence of hearing at the point of the addition.
If the shorter route merely says “ʿan so-and-so”, direct hearing may remain unproved. The supposedly additional intermediary may actually preserve the necessary link. Without establishing the conditions, the longer chain should not automatically be dismissed.