I can't believe no one has latched on to the real problem here. More than likely, he was NOT an independent contractor, but a misclassified employee of his father's practice. I'm willing to bet that an analysis of his "practice" will show he was an employee of his father's practice. I had dental clients years ago who had dentists treated as "independent contractors". I told them that they were at risk, but they continue to treat them as ICs. That is, until they were caught and the 2 partners had to pony up over $100k EACH for all the penalties associated with misclassifying employees. Ever since Microsoft got caught with the same problem, most plan documents have language that says if an employee who was thought NOT to be an employee is found to be an actual employee, they are still not eligible for the plan. Of course, this means the plan now has to pass non-discrimination while counting those individuals as employees. It may not be a problem if they would have been paid enough to be HCEs, but if they only made $100k a year, then they are going to count against all the tests because they are NHCEs getting zero.
Anyway, I think he's taking a big risk in not just crediting time with his father's firm for everyone; I probably would not handle the case if he didn't agree to do that.
Larry.