A quantitative analyst is preparing a performance report of a corporate bond portfolio. For the previous 1-year period, the analyst finds that the return on the portfolio was 4.4% and decomposes this return as follows:

• Return attributable to the risk-free interest rate: 3.4%
• Return attributable to the credit spread: 2.0%
• Loss rate over the period: 1.0%

When observing the portfolio's returns over a 3-year period, the analyst notes that the difference between the portfolio's return attributable to the credit spread and its loss rate remained positive and varied from 0.7% to 1.3% each year. Which of the following would the analyst be correct to identify as the most likely explanation for the persistent positive difference between the credit spread and the loss rate?