TT #216 · Parshas Tazria · Aliyah 5 · Passuk 37
English: If the netek remains unchanged and black hair has grown in it, the netek is healed; he is clean, and the priest shall pronounce him clean.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:37
Torah Temimah cites Sifra (Toras Kohanim) for the continued pure status after qualifying black hair later disappears.
Sifra — Vayikra 13, Midrash Sefer
English: Even if the black hair later disappears, he remains clean.
Textual derivation
Once the stated healing condition has established purity, the later loss of black hair does not undo it.