A Legal defense
It should be noted that one very prominent atty in Missouri uses interesting language regarding the license system for CCW.
He consistently refers to the license as "a defense" which from a legal point of view is indeed accurate.
Carry of a concealed weapon is unlawful in MO. Note that if you have an ENDORSEMENT you have permission to violate that law and would simply have to prove you indeed had obtained, maintained and that the endorsement was still valid if you were to indeed be charged with illegal carry of a firearm.
As has been discussed within this thread, some may feel that there are alternate "defenses" for the same activity. If you find those defense positions plausible, I would HIGHLY suggest you engage in a thorough discussion with your own atty.
Because of the passions on these boards we often get into discussions of legal matters and typically default to "what makes sense" and while you would find me very much in agreement that our country was designed to be regulated through common sense interpretations, once it becomes involved in the opinion system aka the courts, that rule no longer applies. It applies so little that that same atty uses the phrase "it doesn't have to make sense, it is the law" almost every time he speaks of gun rights issues.
I believe much of what has been discussed does "make sense" in so much that the defense is PLAUSIBLE, however, when it comes down to the issue as a whole, it fails the common sense test. If you have the endorsement, it is far less likely you will see charges, but it COULD happen (some numskull failed to enter data into MULES system and officer see's no valid permit) in such a case it would likely be dismissed in short order once good faith information was provided to the court system. If you opted for the other defense, while potentially setting ground breaking precedence and new law, you will likely be heading to several court appearances and will be shelling out huge piles of money, or as the atty mentioned above says, barrels full of fifties.
As mentioned throughout, the wise choice at this point in time for most of us is to clearly follow the law and take the least expensive path in our defensive position, but each and every person is free to deviate as they choose. I would clearly suggest NOT taking legal advice from this forum and consulting an atty of your choosing to develop your own cost/benefit analysis as any misjudgement may result in a loss of your freedom.