Evolution of the orbital parameters of the four planets in the nominal simulation N4. The shaded areas mark the positions of the peri- and apo-centre of the planets, q = a(1 − e) and Q = a(1 + e), respectively. The beginning of the plot up to about 150 000 yr shows the nominal simulation N of Griveaud et al. (2023). Uranus and Neptune are added consecutively in the simulation and the final resonance chain is (2:1, 3:2, 4:3). Here Neptune’s introduction time was T_N,0 = 250000 yr (see Fig. 3). The dashed and dotted vertical lines indicate the time at which the mock disc dispersal is respectively started (t₀) and ended (t_f); see Sec. 2.4 for more details.