The sentence is trying to say that VRDB stores information for three different versions of every file (if the file changes, of course).
I am not sure if saying "doing it three times for each file" wouldn't somehow imply that VRDB checks the file three times and ignores it ever after (which is not true). VRDB checks the file very time the database is regenerated, and if the file is found different, its info is stored. If there would be more than three versions of given file in the database, the oldest ones are forgotten - only the last three are stored.
avast! is lowercase by definition - it's the name of the program.
As for the word "antivirus" - if used together with avast!, it should probably be spelled "avast! Antivirus", but you are right that it's written as "avast! antivirus" often... well, you can say that the word "antivirus" is not part of the name - so it's written with capital A in titles, and with lowercase a in the ordinary sentences.
It should never be spelled "AntiVirus" - and in the program, it never is - where did you see it?