I can't find the mail with Artur Karp's question about later knowledge of the Brahmi script. In this connection I would like to refer to refer to the one of the Nagarjuni caves, namely the one called Vahiyaka, in which the whole word ajivikehi was removed (see Basham, Hist. and Doctr. of the Ajivivikas, p. 157). It seems that the person responsible for this effacement could read Brahmi. Unfortunately nothing can be said about the time lapsed between the engraving of the inscription and the subsequent effacement.