Samson and the contingent nature of prophecy

[M]any of the prophecies in the Bible are, either implicitly or explicitly, contingent upon other circumstances. Furthermore, applying the all-or-nothing hermeneutic of Kramer, one will have to dismiss, not just Micah, but other prophets and even angels of God! For instance, in one biblical account we read:

There was a certain man of Zorah, of the tribe of the Danites, whose name was Manoah. His wife was barren, having borne no children. And the angel of the Lord appeared to the woman and said to her, ‘Although you are barren, having borne no children, you shall conceive and bear a son. Now be careful not to drink wine or strong drink, or to eat anything unclean, for you shall conceive and bear a son. No razor is to come on his head, for the boy shall be a nazirite to God from birth. It is he who shall begin to deliver Israel from the hand of the Philistines.’ Then the woman came and told her husband, ‘A man of God came to me, and his appearance was like that of an angel* of God, most awe-inspiring; I did not ask him where he came from, and he did not tell me his name; but he said to me, ‘You shall conceive and bear a son. So then drink no wine or strong drink, and eat nothing unclean, for the boy shall be a nazirite to God from birth to the day of his death’” (Judges 13:2-7, New Revised Standard Version).

Notice how the angel of the Lord prophecies, without any conditions attached, that Samson would be a Nazarite, free his people from bondage, and would refrain from alcoholic beverages and unclean foods. And yet not a single one of these were fulfilled, as we read subsequently in the Book of Judges. What are we to make of this? Obviously prophecies are, by their nature, contingent upon historical events and individuals [as discussed in the article]