Well, you throw what you can at the wall and see what sticks, right? ;D
But some of the stuff you were saying upthread, and mentioned also in the "Stone Age Atl****s" documentary, about people continuing to make offerings in the form of precious goods (stone axes) when they passed over the sunken Doggerland in their boats. It reminded me a lot of this kind of thing (which you've probably already checked out):
Now, the timescales between Doggerland and Celtic sword offerings are pretty vast, I agree, but I think it's interesting, the idea that the "Otherworld" was underwater/underground and could be accessed via lakes, rivers, the sea etc. Okay, so a lake in Switzerland is not the North Sea, but if one was Robert Temple or somebody, one could postulate in the pages of one's mighty tome that the refugees from Doggerland and their descendants (and there seems to be a lot of evidence now that even if cultures and languages changed over time, it wasn't so much a case of mass colonisation as one of indigenous populations being "converted" by relatively small numbers of migrants) carried on the tradition long after more than the vaguest memories of what they were doing and why they were doing it had faded. All they had was the idea that the gods/afterlife existed underwater, somewhere, and maybe this vague idea continued right into Medieval/Christian times with things like the Hellweg processional routes that you mentioned earlier in the thread.
Plus you can bring the Arthurian stuff into it, which probably sells books!
But yes, it's suggestive anyway. Suggestive of what exactly, well that's a good question. Plus there's the suggestion that Nuada/Nuadu/Nuadha, him of the Tuatha De Danann, was in some way associated with swords and watery offerings. Wikipedia, that fountain of reliable information (!) says that Nuada "is cognate with the Gaulish and British god Nodens. His Welsh equivalent is Nudd or Lludd Llaw Eraint."
Well, according to Wiki, Nodens "is a Celtic deity associated with healing, the sea, hunting and dogs." Dogs again, eh? Moreover, the main Romano-British cult centre for Nodens, at a place now called Lydney Park is situated so that "it offered a clear view of the massive Severn Bore, a tidal wave which, under certain conditions, rises near Gloucester and its position within an earlier Iron Age hill fort must also be relevant."
Okay, the wrong coast and a few thousand years too late, but we're free-associating here, right?
If you read some more of the Wiki articles, you'll also see claims that the name Nuada/Nodens/Nudd might be derived from a Proto-Indo-European root meaning, among other things, "go fishing". And it also points out the similarity between these names and the Norse sea good Njordr. Anyway; some tenuous stuff, probably, but I like this sort of dot-joining exercise...