inmates became stronger with every passing days.
the game wasn't meant to be completed in the first run, even if someone reported he did it at max difficulty and with a pure ending.
Inmates do not in fact get stronger every passing day, they scale up with Karryn, except for the named enemies (with level in their name) who get stronger every time you encounter them.
Other than that, inmates may get boosts from various effects/edicts, but those typically would be player choice to implement.
The game is in fact meant to be completed in the first run, if you know what you're doing.
Having said that, I'm too much of a casual to complete the game on Prisoner or in any challenge mode, but I don't doubt try-hards like that exist.