MANY years ago I collected stamps-mainly US and Israel.As my interests changed to chips and chess sets I sold my stamps. A year or two ago I discovered a box of Israeii first day covers in my basement.
They were on special envelopes with information & seals relating to the subject of the stamp.I took them to a large reputable stamp & coin dealer .He looked through the box very carefully and examined each cover. When he was finished I asked him what they were worth. His answer was "nothing"!