So this is why people take classes. I am working from a kit with a pre-wound warp in two bouts. Pre-reeding the first bout went very well. Using the cross tied into the warp, each group of threads goes under the back lease stick and over the front stick, through the reed, then under the front stick and over the back. But for the second bout, the cross made by the ties goes in the opposite direction - first over the back stick and under the front, then over and under on the return. So the center of the warp would have a doubled groups of threads side by side following the same path through the cross, and the cross on the right side would go in the opposite direction from the cross on the left.
I convinced myself this was a big problem, and set about trying to fix it. Flipping the bout over didn't help. All I managed to do was lose the cross from both sides of the second bout. I should have retied the cross before moving the lease sticks, rather than trying to hold it open in my hand. Reconstructing the cross has been a disaster and an education, but puts me back were I started. I suspect (now) that this difference actually doesn't matter, so long as each separate thread goes under one stick and over the other. If the threading is correct, adjacent threads can follow the same path or opposite paths through the cross with ultimately no effect. Is that right? Is there any advantage to having different bouts switch the direction of the cross?
My reconstructed cross almost certainly puts some warp threads out of order. I haven't wanted to undo the warp chains to check, at least until I've got the warp lashed on to the back beam (warping back to front). When is the best time and method to fix that?