I have a list of approx 500 publications. Each of these publications has a
unique number (ISBN). These publications are all sold individually to
numerous suppliers. In addition, each of the publications may be a part of a
pack which is made up of perhaps 1, 2 or 3 other publications. This pack is
given its own ISBN.

EG

ISBN Portfolio/Product Author
0455221669 Annotated Trade Practices Act Miller
0455223157 Annotated Trade Practices Act Miller
0455223319 Annotated Trade Practices Act Miller

In this example the first ISBN is the individual and the next two are pack
ISBN's. The sales data is held in separate sheets. This data is treated
differently for Pack sales but needs to be consolidated for each month by the
individual ISBN number.

I need to find a way to consolidated the sales data by referencing only the
individual product ISBN.

If this is unclear please let me know or happy to email an example of the
data.