The illustration above shows both sides of a 3¢ brown endwise coil stamp. Notice that the perforations along the bottom edge are on another piece of paper stuck to the back of the stamp.

Single coil stamps with a "tab" or piece of selvedge attached to one side can also be confusing to collectors. Shown above are three sidewise coil singles, each with a piece of selvedge attached to the right side of the stamp.

Both of these varieties exist because of the way coil stamps were made. During the Admiral era, rolls of 500 coil stamps were hand-made by joining strips of stamps end to end. The strips were either 10 or 20 stamps in length, with a straight edge at one end, and a piece of selvedge at the other end. The straight-edge stamp at one end of the strip was simply attached to the piece of selvedge at other end of the previous strip.

The illustration above shows a pair of stamps where two strips of stamps were joined in this manner. A pair of stamps joined this way is known as a paste-up pair and is collected as such. If you look at the bottom part of the photo - which shows the back of the stamps - you will see the stamp on the right has a piece of selvedge attached to it. If the pair were separated into two stamps, one would be a paste-up single, and the other would be a normal coil stamp. If the pair were soaked in water, the stamps would separate into two stamps - one with three straight edges, the other with the piece of selvedge still attached.

Illustrated above are two used pairs of perf 8 endwise coil stamps, each with a piece of selvedge at the bottom. Notice that the bottom cancellations on each pair are incomplete even though there is enough room on the selvedge for the rest of the cancel.

These are examples of coil stamps where the paste-up joint separated in the process of soaking the stamps off the envelope. The missing stamps had the rest of the cancellations on them.

Paste-up singles and coil stamps with a piece of selvedge on them are fairly common. They are certainly collectible and are much more affordable than mint paste-up pairs.