Hi, I’ve recently changed our GL account numbers to new 6-digit series from the previous 4-digit ones. However, our finance team is wondering if there’s a way to generate historical reports (such as BS and IS) using the old account numbers. I’m not sure if this is possible. Would you mind sharing your insights on this matter?

You could create a custom field on GL account for the legacy account number and use that in reports. Another option is Accounting Contexts but that's probably an overkill for this