Dynamics GP manuals and online help state that you can only post transactions to two open years. This is not the case—you can post transactions to any and all open years you have in Dynamics GP.
The following are guidelines for fiscal years and periods in Dynamics GP:
Each fiscal year can have up to 367 fiscal periods.
Fiscal years cannot overlap.
Each fiscal period within a fiscal year can have a different length.
Fiscal year names can only be a four digit year number.
Up to three periods can have the same starting date. This is sometimes, although rarely, used for adjustment periods and is typically not recommended. Best practice is to not have overlapping fiscal periods.
You can make changes to fiscal periods after they have been set up.
You can only post transactions to the last historical (closed) fiscal year. For example, if 2007 and 2008 are closed you can still post to 2008, but you cannot...