Hey guys, I'm trying to import 150k contacts (basically 15 10k CSV's) and I need two files for each 10k file. An ID file (tells the file which existing record to add/update) and a source file (with the data to be added/updated) however this ID file cannot contain duplicates, so once the duplicates are removed I end up with less ID files than source files, so it's unclear what source file goes with which ID file. Any thoughts?

Take your source file and copy/paste the ID column into a new excel file Then use Data > Remove duplicates in excel to shorten the list to unique values Save As PRIMARY FILE 1 and the other as SECONDARY (source) 1

Thanks MGBC