Gather data that don't exist from different worksheets to another workbook

Hi,

I'm having trouble with a macro aiming at gathering data that don't exist to another existing workbook.
In my example, I have two sheets in the file "Input weeks". In each sheet, I have a list of weeks with a code for every days. If the week already exists in my database, then I get a code, but if it doesn't I want to add the new week created in my database "Catalogue weeks" at the end of the table to a new row.

For instance, in the sheet "Mail 1": the week "J000;D139;JRHE;A041;A043;D137;D137" already exists and the code is E351.
But the week "J001;J002;J003;J004;J005;J006;J007" does not exist and I would need to copy this week to the workbook "Catalogue weeks". Then, in the workbook "Catalogue weeks", I would give a code to this
newly created week and I would need this new code to appear on the sheet "Mail 1".

Last but not least, I can have several sheets named "Mail 1", "Mail 2", "Mail 3"... and I would need to loop accross all sheets.

Could you please help me?

If you have any question, feel free to ask.

Many thanks!

Okela