Wait to be told one's unkempt after 9 Av?

Question

I have heard (from people for whom it's been relevant) that someone who may not shave or cut his hair because he is in mourning for a relative, and whose period of mourning ends, nonetheless waits to shave or cut his hair until someone tells him he looks unkempt. However, I have not heard of this rule for the three weeks, when it customary not to cut hair or shave. That is, I have never heard that we wait to be told we're unkempt before we shave or cut our hair after the three weeks are over.

Is or was there such a custom (to wait after 9 Av to be told one's unkempt)? If so, who had it, and/or what authorities supported it, and on what grounds? What, if any, authorities opposed it, and on what grounds?

Answer 1

Nitei Gavriel Aveilus2 3:1 says that the prohibition of cutting hair beyond 30 days is only for a parent, which requires one to be told that he looks unkempt prior to taking a haircut. For one who is mourning a child or sibling the prohibition is only for 30 days and then may cut his hair immediately after the 30 days whenever he wants because the Aveilus has completed. The case of the three weeks is similar to the 30 day period of a sibling where there is no such requirement to wait for one to tell you that you need to take a haircut because the Aveilus has completed.