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?