Can someone explain why the 1876-CC and 1877-CC Trade $1's are up as much as 70% since Feb 1st?

The huge jump is in the low grades and also up to AU55.
What happened on February 1, 2021?
Price history of both coins for 6 months in AU50 grade.
https://www.pcgs.com/prices/detail/trade-dollar/743/grades-25-60
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What about actual prices realized for sales?
Mark Feld* of Heritage Auctions*Unless otherwise noted, my posts here represent my personal opinions.
I would expect that a price guide would be a weighted average of auction prices realized from past months.
But for coins infrequently traded, the prices for all grades might move up or down based on the few that traded
in those past months.
So you can look at the data and see if you find some that are higher?
It's also possible that the weights themselves were changed, or the consider a larger set of coins than those auctioned.
https://www.pcgs.com/auctionprices/details/1876-cc-ms/97042
https://www.pcgs.com/auctionprices/details/1877-cc-ms/87045
That is about what they were trading for years ago when i was putting a set together. They are way rarer in PCGS holders than people think
11.5$ Southern Dollars, The little “Big Easy” set