Rdb, thanks for the link. I’ve seen it before but didn’t remember it. “An important thing I’ve learned is to pull the sinew from the middle.” That could really be a good way of getting more strands and longer ones too. I’ve also come across this link “Preparing Genuine Sinew for Sewing”
http://www.nativeamericanvisions.com/instructions/sinew.htm which also talks about soaking (the whole) sinew in water, like you do. Maybe I should this try this method too.
I tried soaking a small piece of sinew a few days ago. The fibres came apart quite easily but started to tangle seriously. In the link you posted, Mullet asked a question concerning this problem: “How do you keep it from getting tangled together when doing it wet?” I could however imagine pulling the wet sinew with a florist frog or something similar to a comb would help and prevent the fibres from tangling.
Another thing I noticed with the very small dry-reverse-wrapped sample I made for the pic: The twist stays very firmly in place and doesn’t untwist. Even when trying to untwist it a bit it the twisted plies turn back into place. I’ve never seen that before neither with vegetable fibres nor with Dacron. It seems as if the sinew wants to hold to the twist it has been given by the reverse wrap.