Thanks for all the posts.
I have most of Schopen's works, read them many years ago and am slowly re-going through them again one by one. Brilliant stuff.
I have also found an interesting work by Richard Salomon called. INDIAN EPIGRAPHY: A Guide to the Study of Inscriptions in Sanskrit, Prakrit, and the Other Indo-Aryan Languages
Published in 1998 Oxford University Press. I am yet to start this book, but have skimmed through it.
Salomon mentions the Asokan inscriptions and it seems these are in a great many different languages and dialects or variations - at least 3 dialects (Eastern, Western and Northwestern=Gandhari) of Prakrit which is an early Middle Indo Aryan language. The scripts used are also varied and include Brahmi, but also Greek, Aramaic, KharosthI etc.
Salomon mentions that inscriptions in canonical Pali are very rare in India. He also says in relation to Sri Lanka "Pali inscriptions are, somewhat surprisingly, very rare." p 151.