You may have burned the bridge behind you....I agree with cbg your prior employer has no legal duty to complete the paperwork you request ..and you will note the quoted materials address a supervisor signed job description ...and if the offical description was do ABCD and you in fact did WXYZ as you see it, that may compound the problem ?
If you merely singed a few feathers, I might try an in person request with forms ready to execute and one big dose of humble pie ..it's harder to,say no to,somevody face to face. . My feeling is that an external board is not going to stick it's nose into issues about a prior supervision not signing off as you might like.

