I originally suspected that the safe combinations and generated randomly, and that is partly true. They are generated from a pool of, as far as I can tell, around 3 to 4 different combinations each time you play a mission (so if you load inside a mission the code isn’t changed, but if you say restart a mission the code might change).
The different guides I wrote have the number combination that worked for me in them, but that number combination might not be correct for you. You can check the comments on the guides, or alternatively the comments on the YouTube video linked at the end of those guides (which tend to have more comments), but a sure way of finding your number combination is to follow the instructions in the guide about how you find the number combination in the game.
Here is a list of guides for each of the safes I have written about:
- Opening the Safe in the Coldridge Sewers in Dishonored Quest
- Opening Doctor Galvani’s Safe in Overseer Campbell Quest
- Getting to the Loot Cache in the Incinerator Room in the Kennels (Overseer Campbell Quest)
- Opening the Art Dealer’s Safe (Distillery District in House of Pleasure Quest)
- Opening Pratchett’s Safe in Drawbridge Control in The Royal Physician Quest
- Unlocking the Boyle Estate Basement Vault at Lady Boyle’s Last Party
- Opening the Regent’s Safe in the Dunwall Tower and Eliminating The Lord Regent Non-Lethally
- Opening the Safe in the Flooded District Sewers Area on the Way to the Hellhound Pub