Prompted by recent experimental reinvestigations of the Buckingham birefringence of CO, CO2, OCS and N2O, we have carried out our own reinvestigation of the relevant first- and second-order properties entering the electric-field-gradient-induced birefringence effect of N2O and OCS by means of state-of-the-art quantum chemical methods. The computed and experimentally derived results remain at significant variance, also in consequence of a remarkable disagreement between the ab initio and the experimental values of the quadrupole moment relative to the centre of the nuclear masses.