A client of ours asked the following questions. I believe I know the answers but wanted to kick them to the Epi community to feel better about my answers.
There is a number limit to how many versions are kept by episerver, configurable so it can be increased/decreased to suit the customer.
For details read: https://world.episerver.com/forum/developer-forum/Episerver-7-CMS/Thread-Container/2017/4/limit-on-document-version-history/
Here's the official reference in the User Guide: http://webhelp.episerver.com/latest/cms-admin/system-settings.htm > Editing tab > Maximum number of versions
Thank you both for quick answers!
Just so you know ( or may be you know it already) that there is a change log maintained as well (if enabled).