There are relatively few errors in early US stamps. There is the Scott #C3a invert and the 1869 inverts. And a few imperforate errors. Given the billions of stamps that were produced between 1847 and 1920, there are very few errors.

But with modern issues from 1990 onward, there are a lot more errors. Many of the coil issues are known with imperforate copies. There are numerous missing color errors. Die cuts are missing. And if you collect tagged stamps, there are tagging errors. Stamp publications contain periodic reports of newly reported modern errors.

Why is this so? It all has to do with stamp production and stamp distribution.

Stamps were first printed using a flat printing plate. An operator placed a sheet of paper on the printing press, printed the stamps one sheet at a time and removed the paper. After the ink was dry, gum was added to the back of the sheet and then the sheet was fed through the perforating machine. It was a slow and manual operation. There was a lot of indirect inspection going on at each step. It took days or weeks to produce a single stamp issue.

In the 1920s, the USPOD began using rotary printing presses. The printing plates were curved and fit on a cylinder. Instead of single sheets of paper, large rolls of paper were fed into the printing press. These early presses were still slow compared to modern standards. Detection of printers waste still depended largely on human inspection of the final product.

Today, a stamp issue can be printed in a few hours or a few days using modern printing presses. They are quite fast and for the most part, error free. Errors do happen for a number of reasons. However, there is very little human inspection of the finished product. The stamps are printed, cut into panes (or coils), and packaged without much human intervention.

Why don’t stamp printers hire someone to examine the stamps? It has to do with cost. Now that the Bureau of Engraving and Printing (BEP) no longer is the exclusive printer of US stamps, there is competition among stamp printers to vie for the USPS contracts. They need to control costs and hiring inspectors adds to the cost. And modern technology in printing processes does catch most of the imperfect products.

Stamp printers live with a certain amount of errors because the cost is too high to catch them all. Here’s an analogy. Suppose you keep 50¢ in your desk at work to buy a candy bar. Once in a while, someone steals your money. You could spend $1000 on a hidden video surveillance system to catch the thief. Are you willing to spend $1000 to save 50¢? No, it’s not cost effective. Likewise for stamp printers – it’s not cost effective to hire dedicated inspectors to examine every pane of stamps for the few errors that slip through.

I’m surprised more imperforates don’t exist of the modern die cut stamps. When stamps had perforations, it was pretty easy to tell if the pane of stamps had holes or not. With die cutting, it’s not as obvious. You have to look closely to see if the die cutting is present or not. When a USPS employee sells you a pane of stamps, they are going to complete the transaction and move on to the next customer. They are not going to physically examine each pane of stamps they sell for missing die cuts.

Until the 1980s, about the only way to buy stamps was to purchase them from a window clerk at a post office. Yes, coil stamps were sold in vending machines. And you find some imperforate coil issues. I’m sure that window clerks caught a fair share of errors like imperforate stamps and turned them in for destruction. Also, the BEP still relied on a quality control process that involved humans actually inspecting some (or all) of a printing to remove printers waste.

Today, the USPS is moving away from direct sales by window clerks because that’s the most expensive way to sell stamps. Instead, customers can order stamps directly from the USPS over the computer. The USPS introduced booklet stamps that can be vended from ATM bank machines. In short, there is a lot less indirect inspection going on. Stamps are printed and delivered to the end customer with much less human interaction in between. With less humans involved in the distribution, more errors will slip by unnoticed.

You’re unlikely to find inverted color errors any more. Because all colors are printed in a single pass of the printing press, there is almost no chance that a color would be inverted.

Tagging errors are plentiful because tagging is invisible to the unaided eye. As the stamps were produced, the tagging compound was applied by a roller, almost like printing another invisible “ink” on the stamp. If the well holding the tagging compound went dry, then no tagging was applied to the stamps. Since you can’t see the tagging without a UV lamp, no one would know until they checked the well and went, “Ooops. It’s out of tagging compound. I need to add some more.”

As you review the timeline of stamp production methods, I think you’ll find:

• 1847 to 1920, a few errors like imperforates and inverted colors

• 1920-1970, mainly imperforate coils. Stamps were still largely single color issues.

• 1970-1990, imperforates are known for most coil issues. Tagging errors appear with the introduction of tagging. Some missing color errors. Inverted colors are less frequent because multi-colored stamps are printed in a single pass through the printing plate.

• 1990-present. Most errors are imperforates due to missing die cuts. Most stamps are self-adhesive and don’t have traditional perforations. Missing colors can be found on a few issues. Inverted colors are almost non-existent.

Changes in stamp production and stamp distribution have lead to the state of affairs today. Given the billions of stamps printed annually by the contractors, they still do a good job at eliminating many errors. The chance of discovering a true error today is still very small. But I think you have more of a chance of discovering an error today than you did 20-30 or more years ago when there were almost no errors. Good luck hunting!