PROVIDENCE — The McKee administration has determined Rhode Island can retroactively bill Medicaid back to April 1, 2020, for “tens of millions” of federal dollars to help pay the bills of the patients at the state-run Eleanor Slater Hospital, but it cannot do so for care provided more recently.

It’s a complex tale. But it boils down to this: with admissions closed to new medical patients earlier this year as part of then-Gov. Gina Raimondo’s downsizing drive, the state hospital had, by May 1, 2021, morphed into an “Institution for Mental Disease.”

This means: Rhode Island expects to recover millions of federal dollars the state went without between April 1, 2020 and May 1, 2021, amid unfounded concerns that Slater hospital was in violation of a longstanding federal rule barring reimbursement of hospitals where more than 50% of the patients are being treated for mental illness.