can i run a period end if the last 18 months have not been done [closed]

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I am new to a company . As an audit requirement we have to have Sage 50 post depreciation , which I think can only be done through period end ? However the firm has never done a period end . If the first one I do is period 1 of the new financial year , does it matter that previous months have not been done ? Any info gratefully received Thanks