It rather depends on what it is that you are looking for ?
The files in the log or report folder are pretty clear depending on what it is you are looking for. As I said previously the more user friendly info is available form the avastUI, that is generally imported from the raw text files.
I don't understand the concern about chasing update history. The avast virus definitions and engine update is set to Auto, it checks when you first go on-line and every 4 hours after that (free version, can be lowered to 2 hours, the Pro version lower still). So you know that the update check is done automatically.
Should the update check fail, you will get a pop-up to report that, after an update check where an update is available, it is downloaded automatically in the background, when complete you get a pop-up notification and voice confirmation that the virus database has been updated.
So I can't see the need to record all of this, though it is there in a verbose state in the setup.log file.