Is it normal for scan time to suddenly decrease?

So this weekend my scan time suddenly decreased.from one hour thirty minutes to twenty five minutes.  I did not uninstall any files or anything.  Despite this decrease in scan time, the number of trusted and skipped files in each scan decreased from to 36000 and 24000 100 and 10 respectively.  Additionally, a second scan before a database update has not changed the amount of time it takes to complete but the number of skipped files has drastically decreased from 405000 to 53000.

Was there an update that I was not aware of or are some Norton files corrupted?