A suspended sentence works differently from a standard sentence calculation and understanding that distinction explains why the July release date is likely accurate without any additional good time reduction applied on top.
When a judge sentences someone to 5 years suspended to 4, the suspension itself is the leniency built into the sentence. Your brother is only serving 4 of the 5 years, which already represents a 20% reduction from the maximum the judge could have imposed. That suspension functions as the equivalent of what good time credit does in a standard sentence calculation.
With one year already served and credited, he has three years remaining on the four-year suspended sentence. The July release date likely reflects the end of those three years from when he started serving, which lines up with the math if he received full credit for the year served.
The important thing to confirm is that the year of credit was properly applied to his record by the facility. Have him ask his case manager for a time computation sheet that shows exactly how the credit was calculated and what the specific basis for the July date is. That document is the authoritative source and confirms whether everything has been correctly applied.
Assuming the credit is properly on the books and his disciplinary record remains clean between now and July, the release date stands as posted. Three years down with July in sight is genuinely good news and the finish line is visible from here.