Reb Yaakov Kamentzky, Z”L told me that the the hand matzah bakeries in general do not knead the dough very well. Therefore the white specks one could see when cutting open the matza dough prior to rolling out is raw flour. He said further a dough that has white speks one may not gebrukts even if his minhag is to eat gebructs.
See a fuller article on the subject of hand matzas in this weeks Yated on pages 149-150.