Seated Liberty Quarter guys - here's a real NewB question - What does this Briggs Attribution mean?

Just purchased this coin in a group and it was marked as "Briggs 1-B". I do not see any CPK variety other tan a doubled MM, which I do not see. I see it sold in a Heritage Auction for $402.50 - about double the value of "normal" examples. Can someone enlighten me on this?
Heritage archive
PCGS Cert Verification
Heritage archive
PCGS Cert Verification
==Looking for pre WW2 Commems in PCGS Rattler holders, 1851-O Three Cent Silvers in all grades
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EAC 6024
I'm guessing that mine is a the common coin - is that right? But the old high price is still a mystery.
==Looking for pre WW2 Commems in PCGS Rattler holders, 1851-O Three Cent Silvers in all grades
Successful, problem free and pleasant transactions with: illini420, coinguy1, weather11am,wayneherndon,wondercoin,Topdollarpaid,Julian, bishdigg,seateddime, peicesofme,ajia,CoinRaritiesOnline,savoyspecial,Boom, TorinoCobra71, ModernCoinMart, WTCG, slinc, Patches, Gerard, pocketpiececommems, BigJohnD, RickMilauskas, mirabella, Smittys, LeeG, TomB, DeusExMachina, tydye
==Looking for pre WW2 Commems in PCGS Rattler holders, 1851-O Three Cent Silvers in all grades
Successful, problem free and pleasant transactions with: illini420, coinguy1, weather11am,wayneherndon,wondercoin,Topdollarpaid,Julian, bishdigg,seateddime, peicesofme,ajia,CoinRaritiesOnline,savoyspecial,Boom, TorinoCobra71, ModernCoinMart, WTCG, slinc, Patches, Gerard, pocketpiececommems, BigJohnD, RickMilauskas, mirabella, Smittys, LeeG, TomB, DeusExMachina, tydye