I think the small Y is caused by impacted debris in the die. The design features in the die are inclused which let debris pack into them.
Smaller Y is the result of polishing of the die, you can see all the raised polish lines in the field nearby. As the field in ground down the lettering, since the sides are sloped, get smaller. The dies were probably polished to remove a die clash, which are strongest close to the center of the coin, so the area around the Y received more polishing and thus making it smaller than the other letters. The clogged 8 is the result of a die chip where the "post" in the die that makes the center of the bottom loop of the 8 has been broken away. The last coin shows what is commonly referred to as a "ridge ring" and is the result of die wear/deterioration. It is commonly seen on zinc cents. If can appear on other coins but is much less common. Exactly why it forms I am not sure, but I suspect it is due to a flaw in the hardening process of the dies. The outer edge and center of the dies seem to be properly hardened but the ring just inside the edge seems to be softer and with extensive use this ring sinks creating a raised ridge on the coin. Possibly during the tempering of the steel after hardening something causes that ring to have reduced hardness.
