Back to it then:
Abe it is your posts #10501 and #10507 that, for me, represent the extremes which tend to make my head spin a little.
On the one hand we have a culture that had an incredibly strong oral tradition of passing their history and mores down through the generations. Reading this, it seems possible such stories just might survive intact over millenia.
On the other hand, we see politically-motivated "scholars" who aren't too shy to make stuff up to further some agenda. Reading this, it seems possible the entire OLB is a bunch of nationalistic hooey.
I still want to dig to the bottom of de Burcht Leiden.
You bring up a couple of interesting things.
To start with the last: that burght in Leiden dates from no earlier than maybe the 10th century AD.
It's not anything prehistoric.
That post of mine you pointed at is about why Frisians were motivated to concoct an ancient ancestry.
It was quite common back then: we are the descendants of the sons of Noah, we fought alongside with the Trojans against the Greeks, and so on.
And the "oral" tradition you talk about: in times past people didn't read much or anything at all, they just listened to those who did. And from those who told them stories of what they had read, these listeners to their stories in their turn fabricated their own myths.