X-shooter epochs 1–3 (from 1.4–3.4 days post-merger) alongside SOAR (Nicholl et al. 2017) and Gemini-South (Chornock et al. 2017) spectra from 1.5 days. As predicted from the 1.4 day blackbody temperature, the recombination wave passing through the ejecta has not reached the equatorial ejecta, resulting in no emission peak. However, just hours later and through the subsequent days, Sr III has recombined into Sr II throughout the ejecta, forming both a blueshifted absorption valley and an emission peak – in essence, a full P Cygni profile. Modelling the continuum as a simple blackbody becomes increasingly tenuous after the first two days – for example, bluewards of the 1 μm feature, around 700 nm the Y II 4d²–4d5p transitions are expected to perturb the SED (Sneppen & Watson 2023), while UV line-blanketing is likely observationally needed to match the spectral shape below λ ⪅ 700 nm (Gillanders et al. 2022).