The situation will depend on the retailer. In some cases the warranty will be from the original purchase point.
Any warranty is in adition to your rights as a consumer. If the product that was replaced fails after 7 months and you are told it can not be replaced then you can claim that it was not fit for the purpose. A printer, for example, should last more than 7 months. Even though it has been replaced the replacement should still be expected to last a reasonabl length of time.