How abot the 2017? It's the only year with the "P" Mint Mark. The Mint will take it off next year, they did it as a tip of the hat to the 225th anniversry of the mint.
It looks like the coin had a tiny fin that got pushed over. It's not something that I have seen before.
The Lincoln cent series was begun in 1909 to honor the centennial of his birth. Although the intention at the time was to have each design remain in use for 25 years, the wheat reverse ran for 50 years. Here is a comparison of the first and last wheat reverses. This is a business strike 1909 V.D.B and a proof 1958. The Lincoln Memorial reverse was introduced in 1959 to honor Lincoln's sesquicentennial year. Like the wheat ear design before it, the reverse remained stable for the full 50 years it was in use. Although there was a lengthy period when the proofs had almost no definition of the memorial steps, they eventually corrected this to produce a beautiful rendering of the Lincoln Memorial. This shows the first and the last proof reverses, with 1959 at the left and 2008 on the right. (The hyperlinks refer back to my original posts of these years.) 2008 Proof
In honor of the 200th anniversary of Abraham Lincoln's birth, the mint commissioned these four commemorative reverses. 2009 Proofs Birth and Childhood Formative Years Professional Life Presidency