In this day and age, there are many parallels and variations in every release we see. All of these parallels and variations are intentional. Twenty to thirty years ago a few unintentional errors were found in just about every set. Some were corrected and some were not. There even some “hidden” variations based on different printing locations, such as the “Inc.” & “Inc” in 1989 to 1992 Donruss. Sometimes there are even printing variations in the factory set versions.
1991 Topps is well known as a set with about just as many variations and errors as it has base cards. Quite a few of the errors were corrected in subsequent print runs. There are even some variations in the inset borders of certain cards like Doug Drabek and Robin Ventura.
The parallel with the largest number of cards in 1991 Topps is the Dark Back Logo. On the back of the card is a Topps 40th Anniversary Logo. On the base set, the logo is faint or ghosted (see top card in picture below). There is a parallel set where the anniversary logo is printed darker, hence the name “Dark Back Logo.” (see bottom card in picture below).
This parallel does not encompass the entire 792 card set. This version was printed on sheets A and B of the run. There are 255 cards in this parallel set. The sheet designation can be found in the bottom right corner of the card. Listed as either A* or B*
There is a rare version of the Dark Back Logo where the sheet designation of cards from sheet A is listed as A*B*. This dual sheet designation is difficult to find. I probably have about 9 or 10 of these cards. Here is an example of the A*B* designation.
Originally I figured that this logo variation was done as a test and not continued for the sheets that followed. However, the Dark Back Logo cards are fairly common. The print run is not known, but there are even a few error and corrected versions of the Dark Back Logos, such as the Mark McGwire card. On his card the slugging percentage for 1987 was listed as “618” instead of “.618”.