A system produces a bibliographic reference and the student includes it in the assignment. I propose that we look for the source and verify that it supports the associated statement.
In the example, a title may exist but relate to a different problem. The existence of reference is only the first check.
Citing also means correctly representing what the source says. If it cannot be recovered, the limit must be declared and a verifiable alternative sought, without using the academic format as an ornament.