It's fascinating to hear about rare coins like these! The Bicentennial Quarter you mentioned could be the 1976-S Bicentennial Proof Quarter, which is indeed rare and valuable in certain conditions.
However, it's highly unusual for a single coin to be worth nearly $40 million USD. There might be some confusion or misinformation there.
As for the three other quarters worth over $300,000, these could be specific rare or error quarters that have fetched high prices at auctions or through private sales.
Some examples of rare quarters that have sold for high values include the 1796 Draped Bust Quarter, the 1932-D Washington Quarter, and certain error coins like the 2004-D Wisconsin Extra Leaf Quarters.
It's essential to remember that the value of a coin depends on factors like its rarity, condition, demand, and market fluctuations.
While some coins can indeed be worth substantial sums, it's always crucial to verify information and consult with experts if you're considering buying or selling rare coins.