Former B.I. and former B.I. unit supervisor. What you are experiencing is not uncommon. People (former supervisors) leave, companies close, etc. Same with personal references. People move, are busy, freak when they see an envelope with the return address from some P.D., etc.
As suggested, do some of your own detective work. Contact the former employers and references to:
1. Confirm that the company is still in business
2. That there is someone there who remembers you
3. That personal reference contact info is up to date, and that the references have a heads up that they will be contacted by a B.I. about you and that their help is appreciated
If you discover a problem, let your B.I. know.