question on virus definations

why in the avast virus defn folder only the two latest update folders are located??

c:/program files/AVAST Software/Avast/Defn

only the last 2 virus defn folder why?

where are the old malware signatures?

What would be the point in keeping the old one’s as there updated with every new def’s update.
Avast automatically cleans out the old one’s or overwrite’s them.

thanks for the info craigb! ;D