I just noted that there are three different responses here by people named David. So, my original posting should have said that David Sochar hit the nail on the head!
David Waldmann's last response about growth stresses is indeed correct. However, I have seldom seen growth stresses in soft maple, so I did not mention them; it would be interesting to hear from people who have seen SM growth stress and also if they see it more in silver or in red maple. However, stress could be present in SM in a few pieces, but not to the extent that we might see in yellow-poplar, many softwoods, and some other species.
Note that growth stresses will show up when sawing lumber in that the green lumber will have instant warp.
Unrelieved drying stress would typically be much larger than growth stress.
Also, note that the prong test for stress (see pp. 101-102) will almost never respond to growth stresses, so if the prong test shows stress, we do know that we have drying stress. The prong measures transverse or across the grain stress, but such stress is not what causes movement when ripping. However, if there is transverse stress, we do know that the lumber was not stress relieved as it is suppose to be.
Note that on page 102 of the suggested reading, the picture shows both a test for growth stress and a test for drying stress. Because growth stress is not evenly centered from edge to edge, cutting the small fingers, as illustrated, will show the fingers are erratic in how they curve, versus the more uniform curve from drying stress.
When doing the test of ripping a piece in half, if there is growth stress, one of the pieces might curve quite a bit while the other has no curve. With drying stress, the two pieces will each curve the same amount, but in opposite directions.
Finally, I have seen many, many loads of properly dried lumber that have no stress or so little stress that manufacturing of ripped pieces has no warping issues.
Where we commonly see problems is when the kiln operator has not equalized the lumber well enough prior to stress relief, or the steam used for stress relief has excessive super heat which prevents the high humidity required for stress relief from being achieved.
Note that the right column on p. 101, halfway down, has the procedure for checking stress relief while the kiln is operating. (Actually, the kiln is shut down for a few minutes for retrieving and cutting the wood sample, but further delay is not needed.) Without this test, the kiln operator will relieve stress for maybe 18 hours on every load. Yet, each load needs fine tuning on the time, so this test on p. 101 is how to determine when stress relief is done. (A well air dried load will require very little stress relief, while a load dried in the kiln from green will have quite a bit. Higher shrinking woods, like oak, will have more stress than lower shrinking woods like SM. This is why we need to customize the stress relief time for each load.)