I am a law school graduate. What I offer is mere information, not to be construed as forming an attorney client relationship.
I think you really know about conflict of law rules and jurisdiction issues. I am glad you hit all bases because these might be relevant, as far as retroactive pay is concerned.
Can you show proof of the 8-11-00 status change with raise? I..e letter, email, voice mail, etc? If so, good job in keeping this record.
As to getting this money, I would imagine you would be entitled to that and then some (interest, etc) since he did receive the raise and work in that new capacity. Talk to a lawye in employment labor law to straighten this out.
Here is some information I found from the Fair Labor Standards Act:
FLSA Advisor
Wage and Hour Division
Employment Standards Administration
Frequently Asked Questions
When are pay raises required?
Pay raises are generally a matter of agreement between an employer and employee (or the employee's representative). Pay raises to amounts above the Federal minimum wage are not required by the FLSA.
Here is a link to Virginia labor section, for example. Check out the sections I have indicated. I don't think Virginia would necessarily be the right one, but it helps to have it here just in case:
http://leg1.state.va.us/cgi-bin/legp504.exe?000+cod+TOC40010000003000000000000
40.1-29 Time and medium of payment; withholding wages; wri...
40.1-30 Registration of certain nonresident employers with...
40.1-31 Assignment of wages and salaries; requirements
40.1-32 Partial assignments invalid
40.1-33 Certain assignments not affected