Answer :-
They now LT2P between Plusnets RADIUS and the dedicated MSILs, but there are still a few stragglers.
It's mostly only 20CN using WBC shared now.
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I only noticed the changes on a tracert within the past couple of months.
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ETA (Further message)
Person I asked said not aware of any congestion on their part of the network*, but congestion bottleneck these days is the Wholesale VLANs. :/
*Person who told me, does not BS.