IPF Show Cards

I recently started trying to make some sense out of a stack of show cards I had sitting on my shelf. I am at a bit of a loss on how to do this, since there does not seem to be a list of these issues anywhere. For the issue pictured here at the left, Independence 40, I have 15 cards all with matching numbers (0019/1000). Is 15 a complete set? Or are there more? Other cards I have show subtle differences, blue text on the bottom instead of black, or glossy paper vs matte paper, for example. Were these sold as separate items, or were they just sold as the same? Is the fact that multiple different cards with have the same serial number indicative of a set? Or is it a coincidence? I am leaning towards saying they were sold as a set. But, I would still like to know. I sent a mail to the IPF, but it seems they lost there archives, and do not have info from before 1991. At least, I know now that there were none of these cards sold after 1991. Any help would be appreciated.