Modify invoices entered in historical mode

Hi,

I have a friend brought me his business laptop and asking me for fixing the issues in SA 50 2013 pro ver. Here is the issue:

The company is a new business which started in July 1, 2013 ( also fisical yr) with yr end of June 30, 2014. Session date was July 1, 2013. For some reason, he can only lookup sales or purchases invoices dated beyond Oct. 22, 2013. He cannot lookup invoices from July 1 to Oct 21. If he enter the starting date manually, a window will pop up saying "invalid date...".

From reading the previous posts in this forum, I guess this problem is because he entered all the invoices from the beginning of fiscal year to Oct 21, and terminated the historical mode. So, currently he cannot access all the detailed data posted in historical mode.

Am I correct?

If this is the case, my friend wants to modify the invoices he posted in historical mode, how to do so?

Thanks