If you use log page and save numWords, you could look at words_added. That's my general indicator for new download vs update--my words_added column.
I also I use this, but the only place it's useful is in logpage_entries because logpage automatically leaves out unchanged values except on overwrite, so this indicates overwrite always vs 'lots of fields changed':
Code:
add_to_extra_valid_entries:,fulldownload
include_in_fulldownload:title
fulldownload_label:New Download
add_to_replace_metadata:
fulldownload=>^.*$=>Yes