You can create that using functions DocumentPath() and DocumentName() which will return the path where the QVW file is stored and the name of the QVW file. Adding this to the tables you store you can identify which QVW created which QVD files.
Table:LOAD *, DocumentName() AS SourceFROM File.qvd (qvd); STORE Table INTO File.qvd;
Hope this helps
Then you have to analyze which of the QVW you want to have. If they are a fixed number (say 3) you can create Source1, Source2 and Source3 fields, one for each of the QVW files, so at least one of them will always be populated.
Another option is using a preceding load (the Plain files button in the script editor window) will help so instead of using LOAD * you will have all fields loaded, and you will change the actual Source by the new field you create.
Say the file File1.qvd has the following fields: ID, Amount, Source. Your load script will look like
File1:LOAD ID, Amount, SourceFROM File1.qvd (qvd);
Then, modify it to look like
File1:LOAD ID, Amount, DocumentName() AS SourceFROM File1.qvd (qvd);
Hope that helps