The Prestige Investment Management Company sent a report to its pension client. In the report, Prestige indicated that the yield curve is currently flat (i.e., the yield to maturity for each maturity is the same) and then discussed the nominal spread for the corporate bonds held in the client's portfolio. A trustee of the pension fund was concerned that Prestige focused on the nominal spread rather than the zero-volatility spread or option-adjusted spread for these bond issues. Joan Thomas is Prestige's employee who is the contact person for this account. She received a phone call from the trustee regarding this concern. How should she respond regarding the use of nominal spread rather than zero-volatility spread and option-adjusted spread as a spread measure for corporate bonds?