Grade rules sometimes refer to "occasional pieces"—what do they mean by that?
  Occasional pieces means not more than 10% of the pieces in a parcel or shipment. This provision is used primarily to provide for acceptance of minor defects not normally permitted in a grade. These defects, while accidentally overlooked, are not serious enough to justify throwing out the piece when shipping or reinspecting the lumber.

for more information on redwood grades view the Adobe Acrobat version of Redwood Grades & Uses