Devapriya,

Saraswathi mahal's manuscripts are not the only definitive evidences of tamil script. Most of those manuscripts are "urai"'s of ancient tamil literature, and clearly they are'nt the first written versions of the literature.

Usage of olai chuvadi, seems to be common during sangam era. And talks of books lost during aazhi, implies that written transcripts existed. Even if one argues that aazhi is fictional or passed on through folklore, the fact that many more texts existed cannot be contended.

Even in urai's of sangam literature, verses from other books are quoted here and there. Most of the tholkappiayam's verses suggests that the work is not the first grammar text, but rather restating old known rules. All these shows that Tamil had a written script even during sangam era, and it infact predates sanskrit's written script (I remember reading somewhere that sanskrit's first written script is no older than 300 A.D and it is an inscription).

There are several other points in ur post to contend, but only if time and my laziness permits .