Charles Ellicott Commentary Leviticus 13:35-36

"But if the scall spread abroad in the skin after his cleansing, then the priest shall look on him; and, behold, if the scall be spread in the skin, the priest shall not seek for the yellow hair; he is unclean." — Leviticus 13:35-36 (ASV)

But if the scall spread. —If, after the scall had remained stationary for two weeks, and the patient had been pronounced clean, he is brought again because the scall had spread after the lapse of the two quarantines, he is to be immediately pronounced unclean, whether it was accompanied by yellow hair or not.