Last time, I did an identification guide to US postage due stamps. Which prompted a couple of customers to ask why postage due stamps are cancelled like they have been used, but yet they have full gum. This happens on other stamps too, but with less frequency.
First of all, let me say that used stamps with gum do not have any added value. If you had a used, pre-1900 US issue that still had some original gum, there might be some small premium price for that condition. But in general, no. Collectors who like used stamps arenít going to pay a premium price for a stamp with gum. Those collectors donít care about gum. Collectors who like mint stamps wonít want the stamp because itís been cancelled. If the stamp is cancelled, itís a used stamp, period.
In the case of postage due stamps, sometimes a mailer would have a large bill owed for postage due on a mailing. The postmaster would take out the correct quantity of postage due stamps, cancel them, and hand them to the mailer as a receipt of money paid for postage due items. Many times these postage due stamps went into the trash, but some have been saved over time. You occasionally find them today. Postage due stamps couldnít be used for postage. They were used for accounting purposes and if the stamps had gum, it didnít matter.
With ordinary postage stamps, sometimes the gum remains behind. In some cases, the collector may have carefully removed the stamp from its envelope, leaving the gum still attached to the stamp.
This happens with precancelled postage stamps too. The precancel is added to mint stamps before mailing. A mailer would then affix the stamps to envelopes. The envelopes wouldnít need cancelling because the stamps are already precancelled. Without going into all of the gory details, it was once a rule that precancelled stamps could not be sold to stamp collectors. This rule later changed and allowed stamp collectors to directly purchase precancelled stamps from the local post office. However, some mint precancelled stamps did make their way into collector hands. A collector may have been on friendly terms with a local postmaster and was able to purchase precancelled stamps (with gum), despite regulations to the contrary. And in some cases, collectors would find out who the mailer was and would buy leftover precancelled stamps directly from the mailer.
Precancelled stamps are considered used too, whether they still have gum or not.