If you mean the "Quantity Sold" field gets to zero at the inventory closing, that's correct. Closing inventory will result with having this field and others to zero.
You should have considered changing the system date before closing inventory in order to exclude the "quantity sold" of the first two weeks of the new year.
If you have a recent backup, I would recommend restoring your Dynamics GP into the most recent backup just before the Inventory Closing, and changing the system date then re-closing your inventory.
Of course there are other suggestions which may consider updating the fields to exclude the quantities of the new year, but that absolutely need thorough calculation and analysis.Therefore, the restore would be the best option for me