Hi Mike,
The files in Adagio are all opened to permit shared access to the data. PurchaseOrders will back up the files in the state they are in when the backup gets to the file. It is remotely possible that there may be a synchronization issue between different parts of a database (the batch control to the batch file for example), but pretty much all of the necessary data will be there, and certainly in a form that would be repairable if the worst happened.
If you had to restore, we'd recommend touching base with an Adagio consultant just to make sure that the bits were put back together properly. Usually no one needs to lose data entry that has been done.
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Andrew Bates