Smurfin: The DLCs were made long ago I think, check this vid on YouTube => /watch?v=A3FgnjpZWV0 , fast forward to 2:29, it's a gameplay demo back in January 2015. It shows Contract:Missing Miners at 2:29 , it's one of the free DLC.
I think The Fool's Gold was also mentioned in the leaked file back in 2014, copy paste this link to your browser : i.imgur.com/hEhJlBO.jpg , It's under sq107 PIGS NML , side quest 107 pigs no man's land.
The game was once confirmed to have 40gb in installation size on PC, 50gb on PS4/XBOX1 , but it turned out to be 25gb on PC.
A lot of things in this game were constantly changing during the game's development. For example, in one of the 2014 videos, you get the information about Johnny from Dijkstra, not from the granny.