There are a lot of rumors floating around the jail about reduced sentences, early release, etc. The basic rule is that your friend will serve 85% of his/her sentence and then be released on parole for the remainder of the time.
It sounds like he/she received credit for two months and now has 10 months to serve. If you have a copy of the plea agreement, you could look at the specific terms in paragraph 2 which will help you understand what your friend agreed to and how long he/she will serve. For example, if a person is sentenced to 2.5 years, if eligible for early release, he will serve 2 years, 1 month, and 15 days.