Addendum: Production of $π^{+} π^{-}$ pairs in diffractive photon-proton and in proton-proton collisions revisited, in particular concerning the Drell-Söding contribution

We update our analyses concerning the non-resonant (Drell-Söding) contribution to the reaction $γ^{(*)} p \to π^{+} π^{-} p$, now including general vertex functions for the coupling of pomeron, $f_{2 \mathbb{R}}$, and $ρ_{\mathbb{R}}$, to pions. This takes into account the off-shellness of the pions