Intrinsic spectral energy distribution for all the members of the TeV shell SNR club in the GeV-TeV energy range. For the sake of comparison, the SED from the SNR W44 (age ~20 kyr), where the evidence of hadronic emission is secure, is shown by the dashed line. The corresponding parameters used to produce this figure are shown in Table 2 except for W44 where the broken power-law model from Ackermann et al. (2013) is used.