Ok. I know I'm nitpicking. But just wrapping up a run-through of the series again and this mistake of Cornwells gets under my skin every damn time.
At regular intervals through the books that tell Sharpe's story after he leaves India, Guinea's are referred to as "the golden cavalry of St. George" and are described as having the image of St. George and the dragon on them.
But that wasn't so. The sovereign carried the image of St. George(shown above right). The Guinea carried the Royal Coat of Arms (known as a Shield Guinea) or the quartered royal banner (known as a Spade Guinea, shown above left)
The Sovereign was introduced as coinage in 1814 as Guinea's had become too expensive to mint and were worth more than their face value in gold. (The same later happened with the Sovereign, which has been removed from circulation and now serves as "bullion coins" where one Sovereign is worth about £85.)
The use of "British Gold" to prop up the various countries fighting Bonaparte, equip partisans and found rebellions was common, no matter which coin was used.
For all the research BC does, you would expect him to pick that detail up.
End Rant.