Hello there @mashsand, thanks for posting in the Community!
Could you just clarify for me, where were you editing the file from? Were you using the online integrations to edit the file through the website, or locally on your desktop from the Dropbox folder?
The version history for a Basic account is indeed 30 days, so I'm wondering if perhaps the files might have been edited locally and the changes made previously didn't sync with Dropbox.
Also, do you see any actions for the files being edited before from your Events page?
Let me know what you find and we'll go from there!