1988 - Normal issue. Worn Die Strike 1964 - DEFDAM - Definitely Damaged. 4 took a hit in curculation.
The weakness on your 1988 cent is common on a LMC. It is mostly due to the design of the coin. This area of the reverse lines up with Abe's lapel which requires more metal and is easier for the metal to flow into. These coins are struck so fast that the metal does not have time to flow into all the designs features. The hardness/softness of the planchet can also have an effect on this. I do not see this as a worn die issue.