Bally Heck,
The Boeing manual definition is for "severe windshear" ours is for "windshear" so ours could be used to define any measureable, sudden and sustained change whilst Boeing's puts a figure on what it considers to be "severe."
The point I am trying to make isn't so much about the degree of windshear, but whether or not it is actually windshear that is being experienced and reported.
How do you tell the difference between a gust increase of 20kt and a windshear increase of 20kt? A gust will only last a few seconds at most, whereas a shear will continue much longer.
Can the atmosphere produce multple shear lines each with a change in speed of 5kt? I don't think so. What is being felt, especially in smaller aircraft, are the normal changes in wind speed to be expected when flying in proximity to the earth's surface. Some people would call this turbulence rather than windshear.