Many collectors have undoubtedly encountered this problem... you submit two seemingly identical modern cards to PSA for grading, one card comes back the PSA Gem Mint 10 you expected, while the other comes back a PSA Mint 9. You may be left scratching your head after the grading results are posted for your order.
Well, your PSA 9 may be the victim of a print defect or "PD". "PD" is the flaw in the printing process that causes a card to have some degree of "snow", a possible print dot (some print dots come in the form of the well-known "fish eye"), or a print line of some sort on the surface of the card. Often times, these little pests may be the only flaw keeping your prized rookie card from that elite status of PSA 10. As you can imagine, print defects can be quite frustrating for collectors. Many collectors consider each card a tiny work of art and the slightest imperfection may detract from the overall appeal or beauty of the card.
Since eye-appeal is such a large part of the final grade, the position of the print defect may be the determining factor. For instance, if the print defect is located in the background among the scattered colors of the bleachers, the grader may choose not to downgrade the card. On the other hand, if the print dot is on the player's face or another obvious area, the flaw cannot hide and the card will often be downgraded.
There are also many degrees of "PD" that a grader may take into consideration when assigning a grade. Some "PD" may cause a Mint card to receive the "PD" qualifier if the grader feels the print defect is so extreme that the card could not be accepted in a particular grade. For instance, the 1984 Topps #63 John Elway is notorious for having mild-to-severe white print snow across the photo. You will often find a PSA 9 copy of this card with the "PD" designator. As a result, PSA 10 copies sell for a premium.
Sometimes, a card may exhibit a minor printing imperfection that will not affect its grade. If a card has a printing flaw that every known copy exhibits, then the flaw is accepted in the collecting community as simply part of the card. The 1984 Topps #8 Don Mattingly is a perfect example of this. Just above the number 4 on Mattingly's uniform is a 3/8" squiggly print line that is seen on every known example. Many cards with this flaw reside in PSA 10 holders. In addition, the 1983 Donruss #598 Tony Gwynn has a light circle that looks like it is attached to the end of Gwynn's nose. This printing flaw is well known in the hobby as being present on every card and will not keep the card from achieving a PSA 10.
Whatever the flaw, a small amount of "PD" could be the difference between owning a "1 of 1" PSA Gem Mint 10 or one of many that came oh so close!