Note the date on all those articles is the 1st of March. That is also the date on the letter the Russian UN ambassador was waving around from Yanukovych asking Russia for troops. But looking at a
basic timeline... (crude source, but only a rough outline)
Feb. 26: Leaders of Ukraine's protest movement propose legislator Arseniy Yatsenyuk as prime minister. In Moscow, Putin orders major military exercises just across the border.
Feb. 27: Masked gunmen seize regional parliament and government buildings in Crimea. Ukraine's government pledges to prevent a national breakup with strong backing from the West. Yanukovych is granted refuge in Russia.
Feb. 28: Ukraine says Russian troops have taken up positions around strategic locations on the Crimean peninsula. Ukraine's parliament adopts a resolution demanding that Russia halt steps it says are aimed against Ukraine's sovereignty and territorial integrity. Turchynov says he has put armed forces on full readiness because of the threat of "potential aggression."
March 1: Russian troops take over Crimea without firing a shot. The Kyiv government and its Western supporters are powerless to react. U.S. President Barack Obama calls Putin to demand the troops' withdrawal.
So you basically have two days of unidentified gunmen in control of Crimean government building before that invitation goes out. Given the gunmen were aligned with if not actually Russian that does throw the legitimacy of those appeals into question.