The latest news cast further doubt on the country's claims of military prowess.
On Wednesday, Vice Marshal Ri Yong Ho claimed his country is capable of defeating the United States "at a single blow." And on Monday, North Korea promised "special actions" that would reduce Seoul's government to ashes within minutes.
But analysts say the rockets displayed on April 15 are a combination of liquid fuel and solid fuel components that could never fly together. Furthermore, undulating casings on the missiles suggest the metal is too thin to withstand flight.
Each missile was slightly different from the others, analysts said, and they didn't even fit the launchers they were carried on.
"There is no doubt that these missiles were mock-ups," Markus Schiller and Robert Schmucker, of Germany's Schmucker Technologie, wrote in a paper posted recently on the website Armscontrolwonk.com that listed those discrepancies. "It remains unknown if they were designed this way to confuse foreign analysts, or if the designers simply did some sloppy work."
On April 13, a rocket launch that Pyongyang claimed was a scientific mission was a complete failure.
North Korea has long been suspected of trying to field an intercontinental ballistic missile, or ICBM, capable of reaching the United States. But its four launches since 1998 - three of which it claimed carried satellites - have all ended in failure.
The Associated Press contributed to this report.