TT #170 · Parshas Tazria · Aliyah 4 · Passuk 24
English: If the flesh has a burn from fire in its skin, and the raw area of the burn becomes a bright reddish-white spot or white,
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:24
Torah Temimah cites Sifra (Toras Kohanim) for including a burn that has no remaining area into which it can spread.
Sifra — Vayikra 13, Midrash Sefer
English: The rule includes a burn that has no remaining area into which it can spread, even when it covers the whole relevant area.
Textual derivation
Even when a burn covers the entire relevant area and cannot spread further, the verse’s wording includes it.