I think there is a whole area of story here just waiting to be told.
I think it became very clear very early on, that so much of the actions of the Maidan Installed Government were designed to provoke Russia into a Georgia style intervention and for reasons already stated. I think that it is also safe to assume, that given that, on no account was Putin going to allow that to happen, except in the final resort and then it would have been the full monty, as Russia would have had nothing else to lose.
There is a huge difference between Individual regular servicemen volunteering (even being given extended leave to do so) and entire formations crossing the border under orders for combat operations. For all the sound and fury, I seriously doubt that has happened, as to do so, would undermine the position Putin has been determined to maintain and a company would sink it, just as sure as would a Full Army Group.
My deep suspicion is also that one of the reasons why the Novorossiyans were able to turn the tide against the odds, is because the primary objective of the senior command of Ukrainian forces was to provoke the Russian Federation, rather than simply defeat a rebel militia. Due to that, almost insane operational decisions were made in a failed gambit that has cost and will continue to cost them dear.
One of the provocations; which has been fully recorded during the conflict, has been the constant shelling of Russian territory from the Ukraine. Russia declared that they would fire back at offending units, back in June/July and I have no doubt that they have done. It would however, need a very high level of proof to promote those actions to support the accusations of direct fire support from across the border, which have previously been made.
Finally, I keep reading the question, mainly (but not exclusively) from US citizens, how exactly could a ragtag, drunken, pot bellied, local militia defeat the National Ukrainian army? To this I reply: in exactly the same way as a bunch of ragtag yankee doodle rebels managed to defeat the British Empire some two hundred and forty years ago.
