I see that U-106 has a mainly Northern European distribution, and that while it is present together with P-312, more to the south of Europe it is basically absent while P-312 is present in great strength, I wonder, doesn´t that indicate that U-106 was born after P-312? that some P-312 groups spread before U-106 was born, and then it was born in an areaa in which P-312 was already present?
I do remember someone recently doing a variance calculation that made U106 quite a lot younger than S116 but I cannot remember who it was and it seemed out of step with other calculations previously made.
I think though the overlay theory needs more evidence. As I posted, Belgium is interesting in that it might (this needs further study) suggest that the real genetic division was not the Celtic/Roman-Germanic border running through Belgium but (I would suggest) was the non-linguistic Celtic vs Belgic Gaul divide further west along the Seine. The later may be the real division between the high L21/low U106 area and the low-L21/high U106 area. If this difference is pre-Germanic on the continent and essentially corresponds with an intra Celtic division between Celtic Gauls and Belgic Gauls then this could very well also be true in Britain where the divide would have been between Britons and Belgi.