My sincere thanks to all who responded to my question, on and off list. Each reply was helpful, and much appreciated. Perhaps we do have to think that aja was used in a non-standard way in this text, as Matthew suggested, and is in fact equivalent to ajaya/ajita here.

With thanks to all and best regards,

David Reigle
Colorado, U.S.A.

P. S. Sorry for my typos, inconquerable for unconquerable, and śrīpalo for śrīpālo.

On Wed, Aug 24, 2016 at 12:28 AM, Matthew Kapstein <mkapstei@uchicago.edu> wrote:
Dear David,

It may be useful to refer back to John Newman's article about BHS in the Kālacakra. As he demonstrated there,
the author(s) were well aware of Buddhist departures from classical Skt. norms, and regarded this
as intentional, not due to poor knowledge of Skt. If we recall Buddhist derivations of, e.g., arhant from
ari + han, the treatment of Aja you find here as equivalent to Ajita/Ajaya does not seem so implausible,
even if without precedent in more classical usage.
 
best regards,
Matthew

Matthew Kapstein
Directeur d'études,
Ecole Pratique des Hautes Etudes

Numata Visiting Pro
fessor of Buddhist Studies,
The University of Chicago