Your answer is somewhere in the Maryland Sec of States website. It is truly a way to track the boat and make certain that it is paying the correct taxes. They always want their money!
In almost all jurisdictions you do not have to put registration numbers on a documented velle, just a sticker. However, dependent on who the enforcement is done by, you may have a problem. CG will know the rules and you should not have a problem. Local county and DNR are another issue. I have a documented vessel sailing Lake Michigan. I just added the total registration numbers to the boat to save the hassle. You may be totally in the right, but if they issue you a citation you have to deal with it. Rather than take the time to fight the issue I put the numbers on and never get bothered. I could stand on the principle, but I have better use of my time and pick other issues to challenge.
Yes, you are dead on the mark. The government knows all too well that most people will just take the path of least resistance. That is how they get deeper and deeper into our pockets every day. Every law is legal until challenged and they count on that.
As I understand the law, at least from the past, it was illegal, according to the documentation information, to document and also state register. Just because you do not show the numbers does not mean that you are not state registered. To have only sticker displayed is the same as having the numbers displayed also. Another government game. It is all about the money, and always is with government.
I do not display a state sticker. I have the sticker on board and the state registration also. I have not been stopped here in my state. I was stopped in FL recently, by the water cops, not the CG. They were very courteous and asked to see my documentation information. After viewing same they asked about the state sticker. I showed the loose sticker to them and advised them that it was my understanding that a documented vessel could not display numbers or a sticker as that would indicate that the vessel was registered both with the CG and with the state. They were satisfied and left without boarding or further discussion on the matter.
I agree with the OP that they are apparently aware that they may be on thin ice if taken to court. It is that way with many laws. If a successful challenge to the law was made, they would stand to loose a substantial revenue source. They probably do not wish to chance a hearing on the issue and bluff their way around, knowing that most will fall in line.
I have been doing it my way for the last five years, but who knows what tomorrow brings.