Takeover date for pvt ltd

Dear Friends,

A PVT LTD is formed on 04/05/2012. PAN is on same date.

Takeover agreement on 17/05/2012.

Bank account transfered on 04/08/2012.

What should be the actual date for Takover of a Proprietorship to a Company??

(The date of issueing Sales invoice is as on 04/08/2012 ie as on the date of Bank Account takeoover)

PLz Help.