Auto serial numbers across multiple work sheet in a workbook in a particular cell

I need help on the following subject.

Is it possible to create serial numbers across multiple work sheets in a particular cell in a work book, if possible the same no should reflect on the sheet tab. This method would be more useful in generating invoices in excel.
Example : If I open 100 sheets in a work book , If I put serial no 1020 in sheet 1 in cell no c3 the remaining 99 sheets should get serial nos like 1021,1022,1023 etc in the same cell no c3, if possible the same serial no should reflect on the sheet tab, instead of renaming the sheet tab manually for all the 100 sheets.

Presently I am creating around twenty invoices per work book for my company for which I have created an excel file consisting a Macro called “SPELL NUM” which converts number in to text, drop down list in 12 cells, Sum formulas and V lookup formulas in 12 cells.

My work book consists 24 sheets (20 invoice sheets, one summary sheet and three data sheets. The templates between the invoice sheets and other sheets are different, if I run the requested macro, it should not dysfunction the existing macro, dropdown list and other formulas and it should also not disturb the non invoice sheets and its functions

I am herewith sending my sample workbook in which the requested macro has to work only in first 20 work sheets (which have invoice templates) without disturbing the other sheets, existing macro and formulas. Kindly extend your generosity.

Thanks & Regards
M.SUBHAS SAMUEL.