So, a question about Fate Points, declaring details, and retcons.

Specifically, do you allow "declaring a detail" to retcon things (aka, contradict previously established facts).

To be clear, I don't consider a "reveal" to be a retcon - you think the hero's shot, but he opens his shirt to reveal a kevlar vest.  Not establishing something doesn't equate to establishing the opposite of it, in my book.  I'm talking about actually modifying things that have been previously, explicitly established.

Do you allow that, or not?