FAQ 92 lists reasons a post might not be appearing where it should. Some of the bullet points in it explain why your own post might not appear on your friends' friends pages, but one of those explanations is missing. I'd like to see us add something like this to the end of the first point:
[...]Alternatively, the problem may be that the entry is over two weeks old. Entries older than two weeks will not appear on your friends' Friends pages even if they are the latest posts in your journal.(I tried to work it into a separate bullet point but since the points are organized by the "where it should" part it really needs to get tucked in to the first part.)
I think that case is easily as common as inadvertent backdating, if not more common.