I suppose that's right, Don. I guess my comment that only another diver at that same spot would know was just a way of saying that there was no good answer to the question of what the current was doing at a particular spot at 10:10 AM on that day. The closest one could come would be a diver in very close proximity.
On the day in question I got out of a downwelling by heading away from the reef, which is what I have understood to be the best choice. My son also got pushed down somewhere near me, although not as far, and he went toward the reef and we were both eventually able to ascend. He ended up back on the boat while, I ended up being the subject of a brief search by the boats in the area and found by another boat a fair distance from the reef and quite a bit north of the dive site. They didn't know which way I might have gone because of the shifting currents. If I was in the same situation tomorrow I would still swim away from the reef, unless something at the moment made me feel it was best to do otherwise.
I still feel bad that everyone on the boat was quite freaked-out because I had disappeared. By the way, those Gyre maps you linked to elsewhere were quite interesting.