In BusinessWorks, except Payroll, I believe you can post up to one month in the future and 12 months in the past.  You may must allow prior-month posting at Utilities (top menu), System Preferences, the third box from the top.  Set this to "Yes" to allow prior-year posting.

Then make your entries, and reprint all affected reports.  You MAY then want to change the "Allow Prior..." setting back to "No".

You cannot reopen a closed month but you can post to a past month if you have your setting set to allow it (From the Utilities menu, select System Preferences, click Yes under the 'Allow prior month posting' heading.)  In A/R, A/P, C/M, I/C and O/E you can post 12 months to the past.  In GL you can post 24 months to the past.  In PR, you can only post to a past month in the current quarter.  For more information please reference knowledge base article #18022 How to post prior and future transactions