It seems that only one limb needs a bit of sapwood taken off so far. I've started decrowning it carefully going through about 6 growth rings with spokeshave, rasp and scraper.
I've managed to take a reasonable photo, having finally worked out how to stop the pale wood just bleaching out the shot (it was a RTFM problem).
You can see the alternating layers of creamy yellow and whiter wood, the white stuff is more crumbly and scrapes off fairly easily (You can see along the lower edge...) You can see that along the length of the limb the lines of the growth rings run along the bow. It's only near the grip where I go back to the full depth of the sapwood that the rings run across. The picture gives a good idea of what it actually looks like, not a job you can do for long periods without eyestrain! A little and often is the trick and to get the light right. Once the ring you want to follow is exposed , it's not too hard to follow it, but these are rather fine rings and it's easy to go plus or minus 1 ring. I'm just getting it about right, there will be plenty of opportunity to prettify it later.