Unfortunately, the projected release dates shown on the Sheriff's Website are often not accurate. The first thing that I would advise his attorney to do is to call the Sheriff's Deputies at the County Jail he is at. Eventually he will be transferred to someone who will look into it and hopefully adjust the date.
Second, be aware that even though the projected realease date is often inaccurate on the Sheriff's Website, the inmates are usually still released well before that release date, on a date that falls within the statutory time period or less than the statutory time period proscribed by Penal Code 4019.
The San Diego Sheriff's are usually right on with respect to the proposed release date, but that is based on his credit calculations that are in the sentencing paperwork. He wouldn't be getting half time for any offense unless the date of violation was from January through September 2010 and certain other criteria are met. Keep trying his attorney or consider having a new one look into this matter.