The "Guernsey story" you refer to is NOT a concoction of any sort,
Greenbacker or otherwise.
The British Channel islands are independent administrations within the
United Kingdom. The legalese used is "Crown Peculiar". A system harking
back to the last invasion of the mainland by William of Normandy in 1066,
the islands, Jersey and Guernsey, are independent administrations, each
with its own Parliament, the States. They are the last remaining parts of
the Duchy of Normandy.
At least since the Sixteenth century to my knowledge each has created and
issued its own medium of exchange, and created and issued funds for the
building of infrastructure, interest free, and without debt.
What you describe as private banking activity is quite correct. The
struggle to achieve monopoly of money issue by private interests
has been constant, with actions in the Privy Council, the highest court in
the Kingdom, always favouring the States :-)
As for the current efforts to achieve tax haven status, this is a cause
for much concern, for it brings a very long standing system of absent
debt, which in turn allows very low taxation, into disrepute, not least by
people like you who wish to misunderstand for your own political ends.