Can a school know if you have a degree, if you don't tell them?

[JannikTT]

They are going to find out. Most schools will require you to submit all previous transcripts before issuing you a diploma, so even if you initially sneak in and take the courses, you'll get caught out then. So why can't you just neglect to send them the required transcript?

It's called the National Student Clearinghouse. It has records of every school you've attended and a lot of other stats about your school experience. Think of it as a credit bureau for colleges. That would be how that next school discovered Vle045 was already enrolled at Walden. We've had people here complain that they have to send in transcripts from schools where they've never finished a course, because there's a record that they attended. They can also discover (and verify) degrees you've earned and whether you owe money to a previous school.

It can be a bit of a downside to grabbing every random free course offer you see, if it's an accredited school, it becomes another transcript you'll be required to submit, even if it was just a free art course you dropped out of.

P.S. Even if you did manage to sneak through and get your diploma, they can rescind it after the fact if they discover later that you broke the rules.

All of this applies if you are a student with a US degree, seeking to complete another US degree. There is no way a national student clearinghouse based in the US can acquire information about degrees taken in other countries.