HELP - Referencing cells from different sheets using fixed increment

Hi,

See attached where I've created a copy of Sheet1 and added the formulae.

However note that your last invoice is not consistent with the others. This should start on row 161 (i.e. 40 rows on from the previous invoice) and not row 163.

I obviously don't know precisely how you operate this system but if as I suspect you are using it to create invoices to issue can I suggest that you do it differently.
Create a proper database of invoices and have a single row for every invoice, with each piece of data occupying a different column.

Then create a template workbook in which you will manually enter a particular invoice number. The other cells in the Invoice template will all be VLOOKUP formulae which look up the relevant column from the new database.

You'll simplify things immensely and moreover you've then got the basis for a Pivot Table where you can analyse your data in ways you've not even thought of yet.