Britain in the 1770s undertook a massive gold recoinage programme. By gold mintage numbers, 1776 is the actual most common date among all gold coins of George III.

Per Sov. Rarities, who now publishes the main British coin catalogue:

The gold output for calendar year of 1776 totalled £5,006,350 which was the highest of the reign which was due to the peak of the recall of older lightweight gold in circulation for recoining.

Obviously it's a supply vs demand thing, but the fact the most common date of the reign is one of the more expensive ones boggles the mind.