1 to 1 relationship with multiple tables

I have 3 tables:
Tag Library - A table containing barcode information for thousands of pre-printed tracking tags
Item Type A - Table of type A items which will be tagged using tags from the Tag Library
Item Type B - Table of type B items which will be tagged using tags from the Tag Library

Once an item (either type) is assigned a barcode tag, the Item Type table will have a "Tag Number" field which will contain the human-readable version of the barcode from the tag (using the "Get this field's value from a lookup field and don't allow the value to change" in the field settings)

Each tag can be used only once. So, if a tag is used on a Type A item, it cannot be used again in the future, and likewise for Type B items.

I have done some research and determined that I will likely need a join table, but the example I saw only has 2 tables, so I am having a little trouble trying to figure out how to set up the relationships and configure the join table.

Thanks in advance!

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SJS
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