TT #162 · Parshas Tazria · Aliyah 3 · Passuk 22
English: If it spreads in the skin, the priest shall pronounce him unclean; it is an affliction.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:22
Torah Temimah cites Sifra (Toras Kohanim) for the rule that spreading can render the lesion impure after the seventh day as well.
Sifra — Vayikra 13, Midrash Sefer
English: Although the earlier verse mentions the seventh day, spreading can render the lesion impure on later days as well.
Textual derivation
Spreading can establish impurity on later days too; the seventh-day reference does not restrict the rule to that day alone.