Posterior distributions from atmospheric retrievals of six transit datasets of GJ 436 b, five from CARMENES, and one from CRIRES⁺. Panel A: combination of all useful transit datasets from both instruments. This yields the marginalized one-dimensional posteriors shown in the diagonal panels for log₁₀(Z/Z_⊙) and log₁₀(p_c), with vertical lines at the 16th, 50th, and 84th percentiles. The off-diagonal panel shows the two-dimensional posterior density estimated from the combined samples, with contours indicating enclosed-probability regions (we display 68.3%, 95.5%, and 99.7% levels). For comparison, the CCF injection-recovery curve (S/N = 5, yellow) is overplotted in the log₁₀(p_c) vs. log₁₀(Z/Z_⊙) panel. Panel B: marginalized one-dimensional posteriors for the β parameter separately for CARMENES (five transits) and CRIRES⁺ (one transit).