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On the reverse of this aptly named variety, the letters AM in the word AMERICA are close together, nearly touching. What makes this noteworthy is that all Lincoln cents produced from 1959 to 1991 had a comparatively broad spacing between these two letters. The design change was planned for release in 1993, and indeed all 1993 Lincoln cents, both Proof and Mint State issues, are of the Close AM variety.
The year 1992 marks a transitional year. All 1992 Proof coins are of the normal Wide AM variety, as are nearly all the currency-issue coins. But a very small number of 1992 cents from both Denver and Philadelphia are known to have the Close AM reverse. Fewer than two dozen Denver Mint examples are reported, and only two 1992 Close AM cents from the Philadelphia Mint are known. The rare Philadelphia variety carries a catalog value in excess of $10,000.
While the payoff from finding a 1992 Close AM would be akin to winning the lottery, the odds of finding one are slim. In 1992, more than 4.6 billion cents were struck in Philadelphia, and another 4.4 billion were struck in Denver. If a single full die-run were used to strike each coin, the chance of finding a Close AM may be on the order of 1 in 10,000. Based on average attrition rates, probably fewer than 60,000 survive from each Mint. To find one, you need to be deliberately looking for it.
That said, this variety isn’t too hard to spot, and magnification makes the hunt a bit easier. To help with the attribution, there is a second clear difference that distinguishes the Close AM from the Wide AM variety. On a Close AM coin, the designer’s initials, FG, are spaced farther away from the lower right side of the Lincoln Memorial. On the Wide AM variety, the G nearly touches the monument. It’s worth confirming this diagnostic as well if attribution is ever in doubt. Of course, since most coins prior to 1992 are Wide AM and most coins dated after are Close AM, it’s very easy to have coins of both reverse types for comparison.
The reason for all these minor design changes was never explicitly revealed by the Mint. They were likely aimed at improving die life to make the coin easier and more economical to produce. As numismatic author David W. Lange has noted in his Complete Guide to Lincoln Cents, beginning in 1992 such changes as this became a nearly annual occurrence, but most were imperceptible. The most noticeable of the changes has been this repositioning of the AM. Since all the 1993 cents, both Proof and Mint State, are of the Close AM reverse variety, many have speculated that the 1992 Close AM coins were struck as a test run before the change was implemented on full-scale production. Adding further credence to this theory, tests appear to have been conducted at both Mints producing these coins, Philadelphia and Denver.
For circulating Lincoln cents, the design appears to have been an improvement, as the Close AM reverse remained in use until the final year of the Memorial reverse design in 2008.

Excerpt From: Scott Schecter & Jeff Garrett. “100 Greatest U.S. Modern Coins.” Apple Books. https://itunes.apple.com/us/book/100-greatest-u-s-modern-coins/id866701885?mt=11