Zoom on the spectral region around the Li resonance doublet at 6707.8 Å for Coma Ber objects found by us, Casewell et al. (2006, 2014), and Tang et al. (2018), and confirmed as bona fide cluster members in this work. The location of the Li I resonance doublet is denoted with a vertical red line. This feature is clearly detected only in the GTC/OSIRIS spectrum of the lithium L dwarf DENIS1228 (Martín 1997; Martín et al. 1999), but not in the Coma Ber targets.