Was there not a vow where the head had to be shaven? How was that accounted for, as I must guess it was. What brought it to my mind, was in the New Testament, Paul is encouraged to join four men who had a vow, and "Them take, and purify thyself with them, and be at charges with them, that they may shave their heads: and all may know that those things, whereof they were informed concerning thee, are nothing; but that thou thyself also walkest orderly, and keepest the law." EDIT: To explain, Paul had long since told gentiles that they didn't have to keep the law, especially concerning circumcism and dietary things. The apostle James, and elders wanted to show those Christian Jews who insisted on keeping the law, that at least Paul did so as well.
Let me say again how much I appreciate the patience of you and Tez3 in explaining things. It isn't something that we non-Jews often get a chance to ask a Jew about.