A standard 1990 LC struck through grease. It primarily impacted the obverse but a tiny part of the reverse as well: A no date LC struck through on both sides (photo collaged):
The 1925 D isn't a struck through grease scenario. It is a coin that was struck by a very worn die. We see a fair amount of that on cents struck in mid 20s. Thanks, Bill
Yes, it was struck on worn dies, but they also had grease. The "LI" in "LIBERTY" and the "D" is where the grease was. The motto and Abe were due to the worn die.
Sorry but No... grease had nothing to do with what you are referring to. It is purely due to the die being extremely worn. Thanks, Bill