I read this at 5:30am local and thought maybe I wasn't awake yet... so that's a third person that didn't follow the post... I almost deleted it then.
Post also basically restates the "find duplicate wizard" suggested buy TwinnyFo.
I do have a kludge work around for OP as for the import that is causing the heart burn...
Ideally, OP would create a unique key in the excel table, not easy, but best practice...
However, I suspect that adamdaban is using
Ribbon>External Data>Import & Link>Excel
Before import prepare is dataset in Excel
Open the Excel workbook of interest
Select the range of data to import
Name the range in the excel workbook, save, close
Open Access
Ribbon>External Data>Import & Link>Excel
then select the range name to import
If adamdaban names each range by date then OP will have a good idea what data has already been imported.
Another option is to simply link to the Excel workbook instead of importing the data. Can be a bit of a kludge for the SQL; however, one can write SQL against the linked table. I do this for a database where I'm using Excel as the data entry form (yes, I know...) because they want a non-normalized format that I cannot easily create with a form.