Can the measured thrust of a propeller be greater than the max thrust predicted by Froude's theory?
No.

The actuator disc theory for Propellers uses some simplifications, which are grouped into a propeller efficiency factor which normally is between 0.7 and 0.9. This accounts for friction and swirl losses, which are both neglected but very real. Also, the theory assumes equal speed over the stream tube and an infinitesimally small hub, both of which increases efficiency over that of real propellers.

If the propeller uses a large duct, Froude's actuator disc theory would be insufficient to explain all thrust. You might want to explain your measurements in more detail to get a better answer.