How do you know they're unique? I mean, a mint rolled poster (or a mint LB poster) looks like a mint rolled poster, whether it shows up on Ebay, at Bruce's, at Grey's, or anywhere else.
T
T, I use images from buyers and sellers. Any small damage, water spot, etc. is unique like a fingerprint. Take yours for example, there is more than one copy with the foxing in the border but the exact locations of those spots is never the same unless it is an image of the same poster. A linen backed poster will always have the edges trimmed slightly different or the thread slightly off center compared to another. If I can't tell it from another by some method it does not get counted as a unique copy. This has only happened twice so far for them. Before you ask more, yes I studied forensics for a time specializing in identifying things like this, artificial aging, etc. My focus was on metal and fabrics mostly but it translates to paper items very well. That does not mean that I cannot have a copy more than once if the damage has changed over time.
Mark, the ESB quad I would put at only very slightly more common but comes to sale less often.