What do you infer

Sam’s letter is a result of Charley’s imagination. This can be understood from the fact that the letter was enclosed in a first-day cover and addressed to his grandfather. First-day covers are usually sent by a person to himself on the launch date of a particular stamp. This done so that the envelope is stamped along with the date and it remains as a memory for ever. Such envelopes carry only empty letters and are not meant to be opened. But Charley happens to open one of his grandfathers’ first-day covers dated 11^th July 1894 and finds Sam’s letter in it. This proves that Sam’s letter is completely imaginary.