Hi,
without wishing to step on anyone's toes, to assume that a SB was angled
because the wood wasn't long enuf is, well, nonsense.
SB wood was split usually, but not , following the modern myth, to get the
best possible quality, but because it was much faster and easier. This had
to be done with green wood, and the shakes naturally sorted themselve to
length on account of the knots. That is why we see so few knots. Not
because they were cut out. Where wood was sawn, you can find knots. The
thin shakes also had the advantage of drying quickly.  Most didn't give a
d--- about knots, and where thay did matter they were simply patched or
glued back in and fixed with cloth or parchment.
Angled SBs were angled for structural and tonal reasons, not because the
wood wasn't long enuf.
regards,

Bill

http://www.william-jurgenson.com