I have been told that prophecy outside the Bible can change and even then, only God knows the time. This is the dangers of being a prophet or messenger. You might stick your head out and get it chopped off, but the Church needs them. Peace.
Three kinds of prophecies: - Those who can be avoided. - Those who can be mitigated. - Those who cannot be changed.
One of the first things I look for in anyone claiming Prophecy is that they suffer and are rejected, just like Jesus. I think concerning prophecy changing, with most prophecic messages I have ever heard (including the present Marian ones) there is a built in add on clause that goes somewhat along the lines of, 'If you do not change your ways....' So if you notice with Jonas at Ninevah he was angry when God decided to let the city of the hook when they repented. However this is not always so , the nearer we get to the promised day, so to speak, the more things harden up, become more definite. God wants to give us a chance to be saved, to repent .
Yes and I think true, accurate, blow by blow future telling is really not going to happen because knowledge of the future is reserved to God alone, I suspect. What we find out about the future is what we need to know, to help prepare us for things that will come, so they are not too much of a shock, and to encourage us to change ourselves/community for the better, but we will not get a kind of predict the lotto numbers futurology. That I think would be a prideful thing that we will be denied...