The nature and magnitude of corrections to published estimates of the potentials of zero charge E-pzc for Pt(111)-aqueous interfaces obtained by the "CO charge-displacement" strategy are assessed by comparing such in-situ electrochemical data with surface charge-potential information extracted from work function-surface composition data for related interfaces in ultrahigh vacuum (UHV). The corrections involve estimating the excess metal charge densities remaining upon displacement of the aqueous inner layer by chemisorbed CO. While the resulting adjustment to the so-called potential of zero total charge Et. for the Pt(lll)-aqueous 0.1 M HClO4 interface is only small(ca. 25 mV), a larger correction to the corresponding "free-charge" value E-pzc(f) is deduced, yielding E-pzc(f) approximate to 0.2 V versus SHE. A closely concordant estimate of E-pzc(f) is also extracted from UHV-based work function data. The substantial discrepancies in such E-pzc values for the Pt(111)-acidic aqueous interface with those extracted by means of an ex-situ/electrode immersion procedure are also briefly considered in the light of the above analysis.