[larsdangly]

You are correct that DX is fluid (or, rather, adjDX is fluid), and I'm pretty sure the current edition specifies that your action order is always based on your adjDX at that moment.

Another important principle is that you don't have to commit to an action until the moment you perform it. Of course your range of possible actions may be limited by what you did during the movement turn, or by effects on you of other people's actions that went before you. But you are free to choose from among your permitted actions right up to the moment when you execute them.

A third core rule that is unstated but I think implicitly clear is that you can't effectively force another figure to violate rule 2, above. That is, you don't get to wait to listen to what another figure does at their point in the action order and then go back in time and effectively respond to their 'upcoming' choice. A subtle complication of this principle is the case of Defend and Dodge, where you can elect to do those things in response to an attack that comes your way before your normal action. But if you think about it this special case does not violate this third rule.

Putting these 3 ideas together, I think it is clear that your situational modifiers can shuffle you up and down in the action order, but they can't shuffle you 'up' to before the modifier started to apply. That is, if A, B and C have DX 8, 10 and 11, and if C knocks B to the ground at the DX 11 'count', then A can strike at B just afterwards, rolling against an adjDX score of 12 but not going back in time and acting prior to C. I.e., effectively A will fit into a place in the action order between 11 and 10.