The PRSI record shows the years that such contributions were paid. This is different to paying Income Tax. But if he was employed and paying Income Tax then the Employer should have paid PRSI as well ( but maybe they just did not- incorrectly). If however the official record only shows PRSI contributions starting in 1988 then under current rules his “totals and averages”will only start from 1988, thus giving a better result (better average) than if they started the average from 1972.
It is unclear if the proposed change in 2020 will proceed, which would require a total of 30 years contributions to qualify for the full State Pension.