Thanks for the replies. I was under the impression that it was more than just a tech swap.
So let's compare research. We discovered Agri (89), Sailing (149), Mining (74), BW (179), and a good portion of IW (about 250 I guess): total is about 740.
It looks like BAT researched Poly (149), Mining (74), BW (179), AH (149) or Wheel & Pottery (89+119), and is working on Writing (179): total is about 730 or 790, depending on which path they took.
To really do this right, I think you have to calculate the discounts you get for knowing prereq techs, but at least it seems possible that they still haven't finished writing, especially if they researched another tech somewhere.
I think it would be nice to find out what BAT has researched, if only because we need to decide what to research next. And of course we should hammer out exactly what the tech deal involves. It seem we can only supply IW and Agri at this point. The value of their techs (say, AH + Writing + Alpha) would be much higher. OTOH, we should get the better deal because they are "blocking" the worker techs to us.