A brief explanation of File History might help.
This tool creates a number of copies of your data files. To distinguish between versions, it appends a date stamp to each file name. This is what you call a "UTC backup".
While the external backup medium is connected, File History will copy your data files to this medium. When the medium is disconnected, File History will copy your files to a buffer area on the internal disk. This buffer area is cleared automatically when you reconnect your external medium.
If your buffer area is no longer cleared then File History is probably confused, perhaps because you changed or manipulated your external backup medium. To deconfuse it I would do this:
- Create an image of your system drive, using a tool such as Macrium Reflect.
- Do some spot checks to ensure that you could retrieve individual files from the image.
- Wipe the file history folder on your external and internal disks.
- Start afresh with File History.