There was a time where i had a lot of interest in prophecies. Then, as the time passed and prophecies never happened, I concluded that:
1) prophecies are not real and will not happen, because: a) prophets do not have a real capacity to predict future (altought they see themselves as prophets)...b) most of prophets are just liars.
2) some texts are regarded as prophecies because the mass media/authors want that. We have the example of the Mayan "prophecy" that was not exactly a prophecy, but thousands of authors said the opposite because that was good for their pockets.
3) sometimes there are "viral" texts in the web that are regarded as prophecies but they have a different origin and different purposes. I remember the case of 2 guys trying to prove that anyone can make a fake prophecy that will happen, because you can make any interpretation you like from it. So, they wrote an example, a prophecy* created by them, that circulated the web. Years later 11/09 happens and everybody started to say that the prophecy refered before was from Nostradamus and was a prediction about 11/09! Read the prophecy in the end of this post.
So, now I dont believe on any prophecy, prediction, premonition, etc, UNLESS the origin of it can be given to Buddha or a great buddhist master, for two reasons: a real master/Buddha will not lye and some masters have the power to look into the future.
In the given case of the terma about iron birds, etc, I will treat it as hoax because no one is able to find the real origin (just because of that; Padmasambhava was not a liar I suppose). Unless some scholar (with great reputation among buddhist community) can speak from his knowledge and confirm that such terma is real.
* Here is the faked prophecy:
"In the City of God there will be a great thunder,
Two brothers torn apart by Chaos,
while the fortress endures, the great leader will succumb",
The third big war will begin when the big city is burning"