Comparison between low-ℓ angular CMB power spectra, as derived by the Planck Collaboration using both LFI and HFI data (blue points; Planck Collaboration V 2020), by the WMAP team using just WMAP data (red points; Hinshaw et al. 2013), and by BEYONDPLANCK using both LFI and WMAP data (black points; this work). Thin black lines indicate the Planck 2018 best-fit ΛCDM spectrum (Planck Collaboration VI 2020). The BEYONDPLANCK data points are evaluated by conditionally slicing the posterior distribution ℓ-by-ℓ with respect to the best-fit ΛCDM model, by holding all other multipoles fixed at the reference spectrum while mapping out P(C_ℓ ∣ d), to visualize the posterior structure around the peak. For WMAP, the reported BB octopole amplitude is , which is outside the plotted range.