Selective sums of related data can be computed in a number of different ways.
One way is to use ExecuteSQL with a WHERE clause that excludes the records you don't want part of your total.
Another is to add calculation fields that use IF or Case Functions to make them empty if the data from that records is not to be included. Then your summary fields or calculation fields in the parent record with sum functions sum these calculation fields instead of the original fields.
Or a new occurrence of the related table can be used in a relationship that automatically omits the related records you don't want to be part of this total.
And a summary report based on the related table instead of the parent table can compute the needed totals simply by using a find that omits the incomplete records.