Addendum: Phosphine gas in the cloud deck of Venus

We published spectra of phosphine molecules in Venus' clouds, following open-science principles releasing data and scripts (with community input leading to ALMA re-processing, now benefiting multiple projects). Some misconceptions about de-trending spectral baselines have also emerged, which we address here. Using the JCMT PH3-discovery data, show that mathematically-correct polynomial fitting periodic ripples does not lead "fake lines" (probability < ~1%). then can be characterised a non-subjective manner via Fourier transforms. A 20 ppb PH3 feature is ~5{\sigma} compared baseline-uncertainty, distinctive as narrow perturber ripple pattern. The structure FT-derived baseline shows fitting, if unguided, amplify artefacts so artificially reduce significance real lines.