It’s obviously situation specific. Yes, there will always be ambiguous examples where the category might not be useful or applicable. River otters in your area might not be readily assignable to reintroduced, but they are where I live in the Southwest U.S. Consider the reintroduced (in the 1980s) Verde River population of otters in Arizona which is effectively isolated from any other otter populations. No evidence of any extant native otters anywhere close.