Bruce,
We've had this same thing happen with a few clients in the past year or so. You can make the entries to the older years by using the "Account History" function in GL's Edit menu in combination with GVRW.
Because the Account History function doesn't make changes to the next year's opening balances, a number of fields (mostly opening and closing balances) need to be updated in a few different GL tables using GVRW. If there are a lot of accounts to be updated, it can be quite a challenge to get everything in order so that it all passes DIC.
If you'd like to discuss this option, feel free to give me a call.
It seems to be not an altogether uncommon issue. If there's not some structural limitation, perhaps an ability to post back further than 1 year could be considered?
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Ryan Brohman
Kitchener, ON