Help, 1991 Linc Cent "D" Strike Thru Grease?

I think in this case you may be seeing things that arent actually there when comparing the photo to the 1991-D cent. But if it is from a Grease Filled Die more info is below.



There are also errors called a Struck Through Grease filled die (or just "filled die") error.". Grease strike throughs are very common for the most part, they're probably the most common error type besides laminations, and in the past normally only grease strikes which have obliterated large areas of the coin have any decent added value. The exception are coin series which are rarely found with errors of any kind. An example would be a 5 oz America the Beautiful coin, which is a series rarely found with any type of errors. But even for a coin like that, the strike through needs to be fairly large to really add much value. At the moment all these grease strike throughs including the minor ones are however generally selling for a small premium despite some being quite common, and some are more popular than others such as the 2005-p kansas in god we rust , and obviously when enough is missing to entice some of the more serious collectors is where the values tend to be higher.

im also leaning towards the copper clad is compromised and moisture got under and started the corrosion process.
these clad coins have a life expectancy, so depressing to know someone could pay big money for a coin only to find it in a corroded mess in a couple decades.

Thanks to put this example of a scrap YouTube video. Who do this video has no idea about errors or coins. The moment him say "Stamped Coin" I know is just an Flu-Flu.

In 1991 all MM was on the Working Hub, so are no different kind of MM. What this video show it is just some plated bubles.

All cents from 1983 on are electroplated with copper. Cladding is when two metals are sandwiched together with pressure. All dimes, quarters, and halfs for circulation from 1965 to now are clad.