So let's do it for 2004.
First we need to determine whether the agreement has taken effect under Article 4:
This agreement shall take effect when states cumulatively
possessing a majority of the electoral votes have enacted this
agreement in substantially the same form and the enactments by
such states have taken effect in each state.
If the states that have joined so far don't "possess a majority of the electoral votes" then the agreement does not yet take effect. The election will be handled just like it is now. We can dispense with this case since it makes no change in how the election is decided.
If, on the other hand, the states that have joined so far do "possess a majority of the electoral votes" then the agreement takes effect and we need to continue doing the math. So let's assume they did and keep going.
Next we need to see how Article 3 will come out in 2004. Here is the first step from the first paragraph of Article 3:
Prior to the time
set by law for the meeting and voting by the presidential
electors, the chief election official of each member state shall
determine the number of votes for each presidential slate in each
state of the United States and in the District of Columbia in
which votes have been cast in a statewide popular election and
shall add the such votes together to produce a “national popular
vote total” for each presidential slate.
Here are the 2004 "national popular vote totals":
Bush: 62,039,073
Kerry: 59,027,478
Now we go to the second paragraph of Article 3:
The chief election official of each member state shall designate
the presidential slate with the largest national popular vote total
as the “national popular vote winner.”
Looking at the totals from the preceding step, Bush will be designated as the "national popular vote winner".
Next we use the third paragraph of Article 3:
The presidential elector certifying official of each member
state shall certify the appointment in that official’s own state of
the elector slate nominated in that state in association with the
national popular vote winner.
Under this paragraph, each member state will certify all of their electors for Bush.
Finally we determine who wins the electoral college vote. There isn't a provision in the bill for this step because now we're leaving state law and processing a step that is specified in the U.S. Constitution.
When we count the electoral votes in the joint session of Congress in January we are going to find that Bush is the electoral college winner. We don't need to know the specific number of electoral college votes because we know that the states that have entered into this new agreement all certified their EC votes for Bush and we know from the first step above that these states "cumulatively possess a majority of the electoral votes".
So the bill did just what it was intended to do, nothing more, nothing less. It determined who was the winner of the "national popular vote" and then it turned that winner into the winner of the electoral college vote.
That is what it will always do. If you can set up a hypothetical circumstance under which it does something other than that then you will have a point. I'm certain you won't be able to find one but, if you do, let me know.
But maybe the point you're trying to make is a different one so let me get to that.
It would certainly be true that if mostly blue states had joined this agreement then Bush's electoral college win would be by a greater margin than it was under current law. You would have needed at least one red state to join in order for the agreement to take effect in 2004 since the blue states didn't "possess a majority of the electoral votes" by themselves (if they had then Kerry would be President). So let's say that all blue states had joined plus one red state by 2004. In that case Bush would have received
all of the electoral college votes under this system. But the proponents of this bill apparently don't care because their intent was to turn the electoral college into a mere formality anyway -- and that's what they would have done. Bush in this latest case gets all the electoral college votes and is the electoral college winner but the reason he is the winner is because he won the national popular vote.
So should we care that this bill can give more electoral college votes, perhaps even all of them, to the popular vote winner? If the election is not contested then I don't see why we would care. The popular vote winner becomes President and the EC vote count has been relegated to a mere formality anyway.
But in a contested election then we do care. Because the number by which the EC votes are greater than a majority tells you in how many states you need to contest. In 2004 under the old system the answer was one -- Ohio. In 2004 under the new system the answer might have been a dozen or more states that you have to contest, which then becomes overwhelmingly difficult.
So if what this does to a contest of an election is what you are objecting to then I am with you 100%.
When an election is not contested, on the other hand, I have no problem with how the math works. I'm still against it for other reasons but I don't think, in an uncontested election, that it would do anything really awful.