Police stops for tag violations
It is certainly a lawful reason for a law enforcement officer to stop you if your drive-out tag or temporary license is no longer valid, or if it is not displayed in a valid manner. However, if the officer made a mistake and the tag was valid, or if the tag was in fact displayed in a valid manner, then in some states, the pretext for the stop was then invalid.
In some states, the stop will still be held valid even if the officer made a mistake and the tag was valid
In other states, such a stop would be upheld as being valid. In Florida, appellate decisions exist on both sides of this issue. If the pretext for the stop is invalid, so is the stop. In such an event, the charges may be dismissed at a pre-trial hearing.