TT #123 · Parshas Tazria · Aliyah 2 · Passuk 10
English: If the eruption spreads out in the skin, so that the eruption covers all the skin of the affected person from head to foot, as far as the priest can see,
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:12
Torah Temimah cites Sifra (Toras Kohanim) for spreading whether the status changes from impurity toward purity or from purity toward impurity.
Sifra — Vayikra 13, Midrash Sefer
English: The rule applies whether the condition changes from impure to pure or from pure to impure.
Textual derivation
The Sifra applies the rule across either transition in status; the direction of the change does not itself exclude the case.