Peak R-band AB magnitude of the optical afterglows of off-axis merger-induced GRBs in the sample seen from different viewing angles θ_obs/θ_C (coloured points), as a function of the time between the peak of the X-ray afterglow and the time when the optical afterglow vanishes below the magnitude limit m_lim = 26 (red dashed line). Coloured triangles denote VLT/VIMOS, VLT/FORS2, and Gemini/GMOS-S R-band upper limits of XRT 141001 (Luo et al. 2014; Treister et al. 2014a,b; Bauer et al. 2017) and ZTFR-band upper limits of XRT 191127, XRT 191223, and XRT 210423 (Quirola-Vásquez et al. 2023), and additional upper limits for XRT 210423 measured by VLT/FORS2, GTC/HiPERCAM, Hale Telescope/WaSP, and LBT/LBC (Andreoni et al. 2021b; Rossi et al. 2021; Eappachen et al. 2023; Quirola-Vásquez et al. 2024). Grey dashed lines mark the R-band limiting magnitudes of ZTF (m_lim = 20.5), BlackGEM (m_lim = 22.1) and LSST (m_lim = 24.5). Results on the left correspond to the uniform-jet models of the GRB sample, while those on the right correspond to the structured-jet model with θ_W = 2θ_C. We note that the four GRBs with large uncertainties in their peak magnitude in the case of a structured jet with θ_obs ≤ θ_W correspond to those four GRBs that have large uncertainties in their peak X-ray luminosity as well (see Sect. 4.1).