Does the IRS tell us whether a TIN match was exact or fuzzy?

No. The IRS returns only a yes or no on whether the name and TIN are associated, plus whether the TIN is an EIN or an SSN. It does not share how closely the name matched or what name it has on file.

That is why the API exposes tin_matched (true or false) and tin_match_type (EIN or SSN) and nothing more granular. Baselayer passes the IRS result through as received; there is no additional match score we can add.

The IRS applies its own tolerance for minor name variations, so a match does not guarantee the name you entered is spelled exactly as the IRS has it.