Mudsill Plates were invented by Harlen Metal Products after the Northridge Earthquake to increase bolt strength and splitting of mudsills caused by oversized holes, which is a universal code violation. This is further discussed in this trade magazine article.
A bolt with a common round washer resists 840 pounds of earthquake force, put an MSP Mud Sill Plate) on top and it resists 1335 pounds, put it on the bottom and it resists 1665 pounds, and on the top and bottom 2040 pounds. A 143% increase.
FOUNDATION BOLT EARTHQUAKE RESISTANCE COMPROMISED BY OVER-SIZED HOLE
Here are some tests Harlen did on oversized holes