  Detailed information on decay channel probabilities is absent for many high
mass resonances, which are typically included in thermal models. In these
cases, the sum over all known decay branching probabilities is smaller than 1.
Due to this systematic uncertainty of the model, the exact charge conservation
may appear to be violated. We estimate the corresponding number of missing
charge states in the canonical ensemble formulation of the hadron resonance gas
for p+p reactions at the SPS energy $E_{\rm lab}=158$ GeV: $\Delta B \simeq
0.16$ for baryon charge, $\Delta Q\simeq 0.12$ for electric charge, and $\Delta
S=-0.01$ for strangeness. The value of the considered effect is 5-8%, which
seems to be important enough to include it as a systematic error in the
calculations within a hadron gas.
