Willow Run,
Questions: does NTSB have some review process by which it goes to (for example) ALPA with the results of its investigation, before preparing its report, and ask whether such a representative of pilots would add any other data or tests? Does NTSB vet an outline of its proposed analytic framework for identifying probable cause? Does it circulate a draft report to anyone outside the agency for comment before making and declaring it final?
Short answer, Yes. The final report is circulated as a draft to all parties and they are allowed to provide input in the form of 'Submissions'. The NTSB is free to ignore the submissions, however, they form a portion of the docket when the report is released. You may not see the information in the actual report but each submission is in the docket.