When adding or editing an 'item' within a Statement Group, look at the top-right corner of the window. From here you may select either Current Period or any of the specific fiscal periods. This could take care of your second concern - edit the period for each item.

Perhaps it would be useful on the 'Print Statement Groups' window to have the Fiscal Period drop-down available (like it is in Departmental Print) so you don't have to edit each Statement Group item individually. Or perhaps have another option called 'Prior Period' within that selection list.

You can workaround this by signing into Adagio Ledger using the last day of the previous month. Thus when you print the Statement Group, the Current Period will actually select the fiscal period you want, namely the previous period.
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As for your first about numbers not being as you expected, could you provide an example of what you did? IE what field are you looking at, what value/period did you want to print, and what value/period actually printed for you?