> Does any one have any references about the
> development of the 'augment' (to use McCone's term for
> 'ro' and other semantically related preverbs) in the
> transition between Old Irish and Middle Irish?
You might also have a look at the grammatical appendix
to Jackson's edition of Aislinge Meic Con Glinne where's
there's a short note on this on page 103.
Do you have access to _Stair na Gaeilge_? I imagine that
there is some discussion of this in Liam Breatnach's
chapter, "An Mheán-Ghaeilge". Tabharfaidh mé súil air.