Every collector has an album or box where resides the unusual -- that thing not a legitimate stamp or cover, but nonetheless philatelic, no matter to what degree legitimate. In fact, the word legitimate echoes through the years of history of stamp collecting, first most loudly in the United States for the Columbian issue, with it's highest value at $5, though the set of Zeppelin stamps (again the expense complaint, not to mention their extremely limited authorized use -- on flights of the Graf Zeppelin) through to the current baseball press sheets that many collectors are decrying as a contrived rarity produced by the USPS.
Stamp Shows Generate Philatelic Collectibles
But when there is a stamp event, the items that are created are usually accepted as part of the commemoration and celebration of it. Many "legitimate" stamps have been issued at stamp shows, from the popular souvenir sheets for shows like the National Show of 1933, Cipex, the American Philatelic Society Atlantic City show of 1933, etc. and collectors welcomed them happily.
At any one of the bigger national or international shows one can be assured that there will be at least one first day of issue ceremony to accompany the festivities. Often foreign postal administrations will take the opportunity to release stamps at such shows, where exposure assures that the greatest number of collectors know about the issue and will hopefully buy the stamp or its first day cover in person or by mail or online.
But there are the other items like souvenir cards, cinderellas, labels of all kinds, commemorative postcards, semi-official stamps that are the confusing relatives of the stamps that collectors have no doubt about. When you are sharing your philatelic feast with your friends you may wonder if there is a place at the table for these philatelic oddities. But like everything else in stamp collecting, the decision is up to the individual.
Classic Stamp Show Souvenirs
Although stamp shows or governments would overprint a commemoration of a show on existing stamps the first stamp to be actually printed at a show was the ideal stamp of Great Britain's Jubilee International Stamp Exhibition show of 1912. Granted, it wasn't a stamp that could be used to frank a letter, nor a full-fledged postage stamp, but it was very similar to the stamps at the time which showed Royalty - in this case King George V - and was a good solid philatelic souvenir of an important stamp show.
Of course along with souvenir cards and the like are the more usual souvenirs - covers. These might best be termed philatelic event covers (aka show covers) and they are fun souvenirs that often show some historical event of the area in the cachet, along with a pictorial or informational cancel on a stamp that ideally relates to the show. Of course if it is a first day cover canceled at the show, all the better.
Modern show covers are inexpensive and they probably always will be. Earlier stamp first day covers canceled at a show include the National Postage Stamp show of 1933, featuring the Little America stamp. Covers from stamp shows are popular with many collectors: the ones who attended the show must have the cover as a souvenir; those who were unable to attend the show value such items for the you are there feeling they transmit, as well as offer a philatelic historic marking post.
Show Items' Values Beyond Financial
Some collectors are known to take souvenir cards from shows and have their first day cover created on it with the addition of the newly released stamp and the first day of issue cancel. While these are enjoyable items, it is almost guaranteed that they will never be more than curiosities, their value mostly nostalgic.
Most unusual philatelic items will never attain any great financial worth. Their value is in giving stamp collectors a connection to the philatelic community and proof that the culture of stamp collecting continues to thrive through the years.