Trading and Profit and loss ac

This is an accounting issue. Actual cost or fact must be recorded in the books and in financial statements. The critical issue whether there is a closing stock at the balance sheet date. Get the fact. Using the GP ratio to figuare out a closing stock is unacceptable and dangerous. It may only be used as a point to raise a question for whether stock, according to past ratio, should be there or not. The GP ratio maybe very high this year due to higher profit margin, different products sold, different suppliers or customers....You have to check this with these assumptions for rough estimation or simply for indormation.
The best practice is to carry out a cut-off test to match whether sales and purchases are matched e.g. stock must be out for sale made in a period or at year end, if not, there is a closing stock. Goods received in a period or at year end must be treated as stock for sales made after the balance sheet date. Check the subsequent sales and purchases for this matching.

That is a good question. No closing stock, then how can you prepare the Trading and Profit and Loss A/C. As the figure of closing stock is important, the Trading and Profit and Loss A/C cannot be prpared or completed yet.
Or, you may assume that there was no movement of the stock. The closing stock figure is as same as the opening stock in order to prepare a temporary Trading and Profit and Loss A/C. Also, you may check the Gross Profit ratio to make up a close figure.
Still, you should get the figure of closing stock.