Final answer:
The information given does not mention a 'brand new mattress' at an estate sale; instead, a 'canvas mattress' was found on a bedstead after the departure of the occupants and the servants.
Step-by-step explanation:
The question pertains to a narrative context where a brand new mattress is mentioned in association with an estate sale. From the information provided, it is clear that there is no specific mention of a 'brand new' mattress being found at the estate sale. Instead, the text indicates that there is a canvas mattress that was discovered on a nailed down bedstead after everyone has gone. The stacking of 20 mattresses and the scene of the Queen counting them seems to hint at a story or narrative setup, potentially involving a gag with the top mattress being lifted later on.