Merging/copying text with recorded changes

I have tracked changes in two separate documents. How can I merge these documents while keeping the tracked changes recorded (as if I copied both original files together at the beginnning, before I started modifying each, and kept track of changes in the merged document)?

I am assuming you are using Writer? Instead of merging/copying text, have you tried using the menu option Insert → File to merge the two documents, and if so, what was your result?

I see this was posted back in 2013.
I’m still struggling with it.
Do any of you have a solution to this by now?

I wonder if using git with a GUI and keeping track of changes in plain text file (Save as .txt) would work for you. It has many more possibilities and you seem to be keen on keeping track of changes.