It means he will probably get out on that date but its not certain because of the calculation of his credits. If he earns credits he might get out sooner. If he loses credits he might get out later.
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A 'projected date' is just that. It is the date he is expected to be released. A variety of factors can change that date. He could get out earlier for things like over crowding but he could stay longer if he gets in fights or is not a model inmate and lose his extra custody credits.