Good point, which is why it is better to look at the rules of good airmanship, rather than at the various memos. The administration was obviously a bit of a mess.
Although radar monitoring might not have been required, verification of position before descent was, not because of any particular memo saying so, but because of the general principles and practices of good airmanship. If the crew couldn't verify their position visually, the only other available method was radar. And if a radar fix wasn't forthcoming? Then don't go down.