It is possible to distinguish at least five stages of early writing at Susa.
a) tokens and bullae.
b) numerical tablets.
c) numero-ideographic tablets.
d) Uruk IV style tablets.
e) early proto-Elamite tablets.
f) middle proto-Elamite tablets.
g) late proto-Elamite tablets.
More bullae were found at Susa than at any other site. However, the vast majority of these were found during the early excavations and lack therefore reliable stratigraphic information.
Numero-ideographic tablets from Iran can be distinguished from Mesopotamian ones only by the order of the numerical signs and non numerical signs; in Iran the numerical signs follow the object they qualify, whereas the reverse order is found in texts from Mesopotamia. There is no apparent difference between Mesopotamian and Iranian objects from the first two groups (i.e. tokens and bullae, and numerical tablets).
Proto-Elamite tablets, both early and late, can be distingiushed in a number of ways, based on an analysis of structure and content. The later controlled excavations produced some stratigraphic information for both middle and late proto-Elamite tablets as well as tokens and bullae, and Uruk style tablets. Unfortunately, no early proto-Elamite tablets were found i secure context.
Early proto-Elamite tablets are oblong, often made of very dark, fine, clay. The entries are very short, and not well ordered on the surface of the tablet. The structure of the texts is simple.
Middle proto-Elamite tablets are usually rectangular, and flat. The entries line up with rulings, but the entries remain short.
Late proto-Elamite tablets are rectangular, with neatly aligned text. The entries are long and complex (go here for an example). A sub-group consists of near pillow-shaped tablets with slanted lines, and extremely complex entries.