Quantum valebant means as much as it is worth. It is a common count of general assumpsit.
The following is an example of a case law referring to quantum valebant:
The existence of a contract implied in law under a quantum valebant count depends upon whether defendant uses for its benefit any property of plaintiff in such manner and under such circumstances that the law will impose a duty of compensation therefor. [BOND CONSTR. CO. v. MORGAN, 1999 Mich. App. LEXIS 813 (Mich. Ct. App. Aug. 13, 1999)].