DEAR HARRY: My grandfather, who died in 1973, left his stamp collection to my father, who gave it to me as a 50th birthday gift in 2005. Neither my father nor I ever added to it or sold from it. Last year, I took the collection (largely United States stamps) to a philatelists' convention and sold it for $17,300. The problem is the tax basis of the collection. I know that the value was about $20,000 when my father gave it to me because he had it appraised by a reputable stamp-and-coin dealer in New York. We have no way of knowing the value at the time my grandfather died. What do I do on my 1040?