Along the above lines, there's a slide I remember from a presentation about NamUs for investigators:
Issues that Impede Missing and Unidentified Person Investigations, B. J. Spamer
http://www.untfsu.com/wp-content/uploads/2011/02/FVTC-Feb-2011.pdf
As public users, we doubly can't assume any of the above, because we have no information on it.
Unfortunately, I'm pretty sure that we laypersons are supposed to just read "DNA available" and trust that a comparison will be made, and not get into law enforcement's business. The large numbers of public possible match submissions as a result of NamUs have become a source of frustration for many investigative departments, and justifiably so.