USOS is just a tool and it's mostly a matter of how it's configured (for example MIMUW, my faculty, doesn't use first-come, first-serve registration at all) and

USOS is just a tool and it's mostly a matter of how it's configured (for example MIMUW, my faculty, doesn't use first-come, first-serve registration at all) and how various policies are enforced. Stories about students failing to sign up for a previously failed course are mostly urban legends, I believe. The dean's office has the power to override anything that's going on in USOS and they can manually register you for a subject if it's needed for you to graduate.