Need to modify current vlookallsheets function

(ive attached files associated with this problem)

hi there,
at the moment i have 2 files, a master spreadsheet (S1) and a raw data spreadsheet with multiple tabs (S2). S1 contains a list of order numbers, and currently i have been copying over the tabs from S2 into S1, and using a modified vlookup function so it vlookup's the order numbers in S1 with the order numbers in S2, across multiple worksheets.

The problem i have is when i want to import a new S2 spreadsheet with multiple tabs, and bring those tabs into S1 (deleting the already imported S2 data tabs). When I use Vlookup again, and copy and paste the formula down, ofcourse its going to overwrite all the data ive lookedup from previous S2 data.

I need to find a way of modifying the function so that when I copy and paste it again, after importing new raw data tabs, it doesn't overwrite values already in there, and only puts the formula in cells containing '£0.00'.

I hope that all makes sense.
Would really appreciate some help on this, because at the moment the only solution ive come up with is either to copy and paste the formula manually (which would be really time consuming for over 400 records of data), or copy the S1 tab to a new spreadsheet, put the S2 raw data tabs into that, do the search, and copy and paste manually back into the original S1 any new values found....

thanks