It is quite possible that God knows all that is knowable (possible to know) and only all that is knowable. This would mean that Jehovah knows the potential as potential, the indeterminate as indeterminate, that which is necessary as that which is necessary and that which is actual as that which is actual. He also would know the incongruent or false as either incongruent or false. Hence, we could express the situation in the following ways.
(1) If P, God knows that P.
(2) If ~P, God knows that ~P.
(3) If potentially P, God knows that potentially P.
(4) If necessarily P, God knows that necessarily P.
And so forth. If I had more time I would refine these statements. Nevertheless, you should get the basic point: God knows the potential as potential or God possibly knows what is knowable. So if Adam and Eve had the potential to sin and their apostasy was just possibly or contingent (not necessary)--then God knew about Adam and Eve's deviation as a potential or contingent event (not as an actuality).
My position is not that God was required to act before the Fall if He knew that Adam and Eve would sin. Rather, the problem I have with many accounts of the Edenic Fall is that if Jehovah knows an event will surely happen prior to its occurrence, then it seems that we live in a deterministic universe and libertarian free will is evidently illusory. But quantum mechanics indicates that ontological contingency (indeterminacy) is part of our ontological experience (the subatomic cosmos is likely contingent, even if we cannot prove that the macrocosmic cosmos is too). Now if the cosmos is contingent and if ontological contingency is not an illusion, then God evidently knows the contingent nature of the subatomic cosmos as contingent (i.e., Jehovah does not know the subatomic cosmos as necessary). I believe that the same principle applies to human existence, which is highly contingent.
Conversely, if God already knew that Adam and Eve would fall away spiritually before He issued the command at Genesis 2:16-17, then knowledge of the Fall was apparently possessed before that divine warning and God's knowledge would have preceded Adam and Eve's opportunity to make their own choice regarding the tree in the midst of Eden. But I might simply point out that if God knew Adam and Eve would sin before they disobeyed Him, then it appears that Adam and Eve had no other choice but to sin. For if Jehovah knows at T1 that I will have a math test on quadratic equations at T2, then I will have a test on quadratic equations at T2. If I did not have the test on quadratic equations at T2, but God knew that I would have the test (i.e., He knew it as a necessary event), I would thereby falsify what God knew at T1.
Applying this principle to Adam and Eve: If God knew that the Fall was an actuality before it happened, then how could it not happen? If G (an omniscient Being) knows that at T1, Jones will cut his grass at T2, then it seems that Jones must cut his grass at T2. If Jones changes His mind and decides to go fishing at T2 instead, he would thereby falsify the belief that G held at T1. But since G is an omniscient Being, beliefs that G holds cannot be falsified. So Jones (or Adam and Eve) has no choice but to cut his grass at T2 if an omniscient G holds that Jones will act thus.
[I also want to clean up the "Jones" part, which derives from a work by Nelson Pike]