I can only put a window on it. When shopping in 2004, TTs still had a RVIA weight sticker. By 2007 they had a NHTSA weight sticker that used different definitions for some of the terms and accuracy requirements for what was on the label.
I'm not sure this means every trailer is now weighed at the factory. Most manufacturers can produce an accurate NHTSA label based on engineering standards, just as automobile manufacturers do.