One of my ultimate purposes is to contribute to the revised OED due out in 2005. For a paper I am currently working on, I'm requesting comments and contributions. A summary will be forthcoming. It is the theory that is set forth in the OED and has never been questioned. The feminine H-stem, according to this accepted view, was displaced in the language in a wave of cultural diffusion when the feminine pronunciation began to approximate that of the masculine pronoun in the 12th and 13th centuries.
Many manuscripts use BOTH forms.
The manuscripts are copies of copies of copies. It had NOT dropped from speech and become archaic by 1300. It is scanty and scattered, but nonetheless there. The H-stem feminine held wide currency in the colloquial of the middle ages and therefore, supported by other evidence, was not unknown to the prescriptive grammarians a few centuries later. An explanation for the replacement of the H-stem plural nominative by THEY, a replacement occurring earlier than the other pronouns in question, has never been proposed.