If a user enters an invalid license he'd get informed. Now we have a new case: most likely many users will enter their valid 4.4/4.5 license key into new 5.0 EE. As we now have licenses bound to certain versions, this won't work. Hence the user should get an explicit info that e.g. that his license is only valid for previous version or for the 4.x series so he knows what to do.