Redshift distributions assumed for our stage IV synthetic galaxy samples, with LSST year-1-like photometric tomography (top; Sect. 3.2.1), supplemented by DESI-like spectroscopic galaxy samples (bottom; Sect. 3.2.2). Vertical dotted lines give the redshift edges where the full photometric redshift distribution (top panel; black curve) is cut into tomographic bins (hard-edged histograms). These distributions are convolved with Gaussian kernels of width σ_z = 0.05(1 + z) to produce the true redshift distributions (solid coloured curves), and then displaced with randomly drawn shifts, δz_i, as $n_i^{\mathrm{shifted}}(z)=n_i^{\mathrm{true}}(z-\delta z_i)$ to define the ‘shifted’ distributions (dashed coloured curves). Apparent small overlaps of similarly coloured histograms in the bottom panel are plotting artifacts.