So you could delete all the files from 'Documents\Avalanche Studios\COTW\Saves\76561198026591555' and move all the files from folder 0 into that folder and then delete or move the slots folder out of the save folder.
Example (found inside slots folder) folder 0 could be Hirschfelden and folder 1 could be Medved Tiaga and if you then went on Layton Lake that would be saved in folder 2. Sadly they are not named and go in order of you entering those reserves. I believe the save files in 'Documents\Avalanche Studios\COTW\Saves\76561198026591555' are from your last save and are what is used when you load your game and the files in each of the slots are the saves for each individual reserve. Before you do any of the following please backup your save folder and disable cloud save.