Collectors keep loving slabs. Third-party grading has brought enhanced transparency, liquidity and confidence to the rare coin market. Perhaps in recognition of this, collectors covet rare encapsulations from grading firms, especially Professional Coin Grading Service and Numismatic Guaranty Corp., and these unusual slabs have become collectibles in their own rights.

At a Sept. 18 auction by Great­Collections, the online auctioneer sold a 1946-D Walking Liberty half dollar graded Mint State 65 by NGC for $3,740. For reference, a normal Gem Uncirculated example of this date sells for around $100, nice MS-66 examples can be found easily for $150 and MS-67 examples routinely sell for around $1,000.

What made the brilliant half dollar special was that it was housed in an old “Black Label” NGC holder that was used by NGC only between September and November 1987. The coin’s orientation in the slab is different than what collectors expect today in that the identifying label is placed on the reverse side while the gold NGC logo is on the obverse side.