Is there a more comprehensive Old Persian lexicon than R.G. Kent's?

Hi,

I've been trying to decipher an inscription (apparently) in Old
Persian that formed part of a treasure hunt contest some years ago.
While I am pretty sure it is O.P and not any other sort of cuneiform,
I haven't had any luck with R.G. Kent's lexicon. Added to this is the
possibility that the "message" was a red herring.

Does any other lexicon, in particular a more coprehensive lexicon,
exist?

Thanks,

James McLaughlin.
.

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