The 'Harvey inflation' is no longer referenced in Julia Crick, Elisabeth van Houts - A Social History of England 900-1200 - Cambridge University Press 2011, ISBN 978-0-521-71323-8 (see cambridge.org/us/academic/su ... ?format=HB ).
Reading this book online is possible via books.google.de/books?id=mM6OA8 ... er&f=false .
You find there:
By the last decade of the twelfth century, silver from the north Pennines had declined to insignificant levels. Prospecting on the Welsh borders ... failed to find new sources and the only productive mine, near Basingwerk in northeast Wales, was probably under Welsh control. Thereafter, local sources of silver were to play only a secondary role in the English economy and it was tin which would dominate metal production.
By the end of our period in 1200 the economy was increasingly commercialized with a strong silver-based currency and, although the peak in English silver production had passed, the search for new resources was beginning.
So no inflation then.
Of course (see also https://forum.atlas-games.com/t/the-break-room/102/1 ) this was not the state of the art in 1999, when Heirs to Merlin was written. So Heirs to Merlin reacts to 'Harvey inflation' - or its discussion - by having Stonehenge magi cause their own inflation. This shows the research that goes into the ArM books.
Also (see Card & Board Games ARCHIVE & LINKS ) Stonehenge covenants were indeed liable to 'political spending' at the very end of the 12th century, which - if excessive - could well have caused an inflation.
Cheers