It could be, as Drake’s logs were kept by the Crown upon his return, and lost in the 1666 Great Fire (apparently; lots of stuff apparently was). Various summaries of his voyage have survived, but they lack both exactness and the kind of persistence that would have come from repeat voyages.
Of course, coins tended to stay in circulation for a very long time, so it may have been lost long after, as well. Might be worth another look, for artifacts.
http://www.google.com/search?q=francis+drake+landfalls+site%3Afreerepublic.com
But his description of the “bay” survives, and it matches San Leandro Bay, not Inverness.