This international graduate student (on a scholarship) got a SSN and had to file taxes every year while in the US. In May of his last year, he graduated. Return

This international graduate student (on a scholarship) got a SSN and had to file taxes every year while in the US. In May of his last year, he graduated. Returned home. On Jan-Feb next year, the school mailed him the tax forms to his country for the previous fiscal year's taxes. He never completed those forms and did not file them with the IRS. He's living his life in his home country now. He lost his SSN card and he doesn't remember his SSN. 20 years later, he wants to return to the US as a tourist to visit some friends. Would that tax mishap be a problem for him? Thanks in advance.