This 1999 Lincoln appears to be struck by a second very weak strike.

[Sberry002]

This 1999 Lincoln penny received a normal first strike and a slightly adjusted very weak in the collar second strike. (I think)

[MintErrors]

In my opinion, its a bit difficult for me to assess this coin. I think i see die deterioration. Die deterioration is a working die just about at the end of its service life. Its not new and sharp anymore. Lincoln working dies can strike close to one million cents. Its a metal vs metal challenge.

Zinc cents are prone to having the thin copper layer being split/broken during a strike. When that thin copper layer is split, it often exposes the zinc center. The zinc can escape and in the end can make the surface of the coin look stained. The color can resemble a blue or silverish type stain.

There seems to be a die chip on the reverse rim, to the west (left) of the memorial building.

I am leaning toward this being some sort of machine damage. But, it could be both split plating damage and die deterioration. The letters of UNITED STATES OF AMERICA are inconistent in height, they look like a good candidate for die deterioration.

If this was a double struck coin, evidence should be present on both sides of the coin. I personally do not see anything that points to a double struck in collar error.

I have not thought about a doubled die until just now. Its late. If i find the time to look this over one more time to see if there are any DDO's or DDR 's listed for this year. If you would like, you can look at:

Http://varietyvista.com

[Sberry002]

What happened here is after the first normal strike, a second strike stopped completely above the height of the first strikes letters. The coin moved slightly in the opposite direction of the T in united. The only place that contact was made was by the field just below the rim and the coins inner most rim.

The effect was to push material from the inside edge of the rim into the reverse die letters.

Because the weak strike did not completely close on the coin, material from the carving of the inside of the rim flowed into the unrestricted space between the coin and the reverse die.

There is an impact on the obverse rim edge from this second strike.

[occnumis2021]

the effect, as it looks to me from the pics, is known on coins back to the very beginning for USA coinage. (perhaps earlier on foreign coins)

can't remember the term just now but if you look at old large cents, capped bust halves, perhaps early silver dollars, you'll see that "divot" in the middle of the top of letters.

so it has more to just do with striking than anything else if it can plague coins from 1793-present considiering all the manufacturing changes over the centuries.

i'll post here if i find that term or it occurs to me, unless someone beats me to it.

this has also been posted here before. not your coin but the effect. almost always same stuff, over and over. eventually you just about see it all. XD

[occnumis2021]

you will see A LOT of anomalies on coins, especially in the legend to the rim area all across numismatics.

here are some examples of what i'll just call "striking anomalies" and they can be on the top, bottom, left, right etc of letters, numerals etc.

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[Sberry002]

Weak over normal coin shifted.jpg Maybe this helps