Copy from different workbooks into one and check for unique records

Hi guys, I'm trying to figure out a way for my code, could you please help me? I'm trying to get some reference data from several workbooks( all in the same folder) and check if they are duplicate or not. I want to open the folder, get the reference ( which is always in cell A1), check if it is already in the range of previously checked references ( that is , in another separate workbook, where I will record all references) and if it isn't, add it there and start doing some computations with the data from the referenced sheet (irrelevant at this stage). This is because I may add files over time in the folder and I want to be able to run the code on all of them, without running it twice on the same one.

Here's the code

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Many thanks! I attached some sample workbooks with the references in A1