In his 09 Sep 03 - 08:48 AM post, McGrath of Harlow wrote "...all that a reference to a particular event or name can prove is that any version of the song that includes that does not precede a particular date".

If I understand this point correctly, it means that if a rhyme {or a song} includes a referent to an actual event, we know that it couldn't have been composed before that event occurred. Is that what you meant?

As I read McGrath's comment, not quite. There is a difference between a song that almost entirely about an event, like a battle, and one that contains a reference to it. Certainly, that *specific version* can't be older than the event, but basic song could be. This is particularly the case with children's rhymes, which are much more about the children entertaining themselves than about telling a specific story. As a result, the basic song can be appreciably older than any passing reference it has picked up.