TT #98 · Parshas Tazria · Aliyah 2 · Passuk 6
English: And the kohen shall see him on the seventh day a second time. And, behold! the lesion has become dimmer, and the lesion has not spread on the skin, the kohen shall pronounce him clean. It is a mispachath. He shall immerse his garments and become clean.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:6
Torah Temimah cites Sifra (Toras Kohanim) for how intervening changes in intensity or size are treated at the time of examination.
Sifra — Vayikra 13, Midrash Sefer
English: If it became stronger and then dimmer, it is as though it never became stronger; if dimmer and then stronger, as though it never dimmed; if it contracted and then spread, as though it never contracted; and if it spread and then contracted, as though it never spread.
Textual derivation
For the ruling, later changes cancel the earlier fluctuation: the examiner assesses the lesion’s present state rather than treating every earlier intensification, dimming, contraction, or spread as still operative.