There is a rule, but difficult to see.
For FPs, national scheduler takes up applications in the order of RDs, but, depending upon the ASC area one belongs to and the load at that ASC, one may be scheduled later than another person with a later RD. Thus it looks random if we ignore the area to which the applicant belongs, but, if you analyze the cases of the same area, you see a pattern. For example, all of us who filed in March 2001 in Dallas area, have gotten our FP notices in Feb. last week or March 1st week. However, there are always some exceptions. Sometimes, applications could be misplaced. In some other cases such as a child approaching 21, lawyers may go through liason and get the cases expedited.