The authors comment upon two recent works of Zheng et al. concerning calculations of spectra of light nuclei in shell-model calculations with no core. A critical review is given on the calculation of the effective Hamiltonian, which in these calculations is restricted to the G-matrix. Depending on the choice of the Pauli operator, many-body terms arise which violate the Pauli principle and must be corrected by effective three-body forces. It is demonstrated that the uncertainty in the calculated energies due to the optimal choice for the Pauli operator is as large as the typical correlation energy obtained from configuration mixing involving more than one major shell. Other sources for effective many-body forces and the non-hermeticity of the effective Hamiltonian are also discussed. 9 refs., 4 figs., 1 tab.