https://www.walkermn.com/news/chapter-693-vikings-in-the-tur...
https://sites.google.com/site/stonebankorg/fabulous-nd/moori...
From memory, they were linked to Vikings as mooring stones due to the similarity between the holes found in the rocks here in the US and similar holes in rocks present in Scandinavia that are known to have been used as mooring stones back in the day. I had never seen an example from either place though.
Recognizing the obvious glacial history of the region and the present absence of any large body of water in the region and after seeing this example, I wonder if the hole in that rock is a natural hole formed by weathering of one of the less-resistant minerals from the boulder.
I ask because the boulder appears to be a granite pegmatite and there is a natural mineral that forms large roughly triangular cross-section minerals in granite pegmatites. That mineral is tourmaline. I think if you check that boulder and others like it you could rule out a natural origin if you find no evidence of tourmaline in the boulders.
The lichens could also be used to date the weathered surface of the boulder since they have a fairly well-known growth rate and you could calculate the time since a fresh surface from that.
Also, for the "mooring stone" hypothesis to hold any water one would probably need to know where each known example is in relation to known present-day waterways and to remnant erosional features and ancient shorelines. If they all can be established to have been located along a known ancestral shoreline, especially if you could do a geomorphological reconstruction similar to a palinspastic reconstruction and they all came out on a shoreline that would lend credence to the theory.
From the things on your links, I'm not sure that any of them could be contemporaneous even within a few hundred years of the recent past when we know Vikings were in N America and free to travel and explore.
Cool story though.