Reserving N numbers… these companies suck!

While it's true that anyone could make up a serial number, if on request, they can not produce any documentation that an aircraft is being built, they lose their reservation and any money paid in. Another possible add-on is to limit the number of reservations that a non-manufacture can reserve to a small number. Maybe 5. Not sure why person or business would need to reserve more than 5 N-numbers.
In some cases, those building from plans couldn't show the required documentation. One can download the plans for some types (like the Fly Baby) for free.

In 1998, there were over a thousand Bensen Gyrocopters in the US registry. There were more Bensens than any model of RV (most-common was the RV-4, with ~800 listed).

Today, that fleet of Bensens has been whittled down to just 47 aircraft (compared to over 900 RV-4s, which aren't the most common model anymore). This is mostly due to the FAA re-registration process started in 2010.

Now, I don't think there are a thousand scrapped Gyrocopters out there. I'm guessing the first step in the building manual was "Obtain a registration number from the FAA...."

Ron Wanttaja