(1) I don't understand why some sites are called early Harappan because these sites are pre-Harappan so why we use wrong name with that. Can any one explain?
From 'India's Ancient Past' by RS Sharma, Ch. 9: Chalcolithic Cultures, p67:
Chronologically, there are several series of Chalcolithic settlements in India. Some are pre-Harappan, others are contemporaneous with the Harappan culture, and yet others are post-Harappan.
Pre-Harappan strata on some sites in the Harappan zone are also called early Harappan in order to distinguish them from the mature urban Indus civilization.
Thus, the pre-Harappan phase at Kalibangan in Rajasthan and Banawali in Haryana is distinctly Chalcolithic. So too is the case with Kot Diji in Sindh in Pakistan. Pre-Harappan and post-Harappan Chalcolithic cultures and those coexisting with the Harappan have been found in northern, western, and central India.An example is the Kayatha culture c. 2000–1800 BC, which existed towards the end of the Harappan culture. It has some pre-Harappan elements in pottery, but also evidences Harappan influence. Several post-Harappan Chalcolithic cultures in these areas are influenced by the post-urban phase of the Harappan culture.
(2) Harappan civilization has the following phases:
(1) pre-Harappan (2) Early Harappan (3) Mature Harappan (4) Late Harappan (5) post-Harappan
So, when excavation begin, in the first soil layers we get post-Harappan culuture, and then Late, then pre, and so on.
But, if we combine pre-Harappan layers into Early Harappan (as above), we lose the distinction between the developing and the developed state of the civilization. Does this not lose information that would tell us about how the valley developed?
(3) and here, Harappan zone means area around the Harappan city, am I right??
(4) I have also provided diagram what I understand until now. Is this correct?