The Open Door sport is not a single sport as popularly believed but a pair of slightly different stamps . As can be expected, the ground level door is slightly open, more so on one stamp than the other. The original idea was a series, from just off the latch to wide open, but this appeared to be too complicated and bound to run into trouble. The printing itself may not have been of sufficient resolution to capture the differences.
One pair, as a partly perforated example (the perforations at the bottom of the stamps is missing) has made it into a Discworld stamp collection from a prize ticket in an LBE, but there are others around - in terms of rarity they will rank with the very rarest Discworld Sports such as the Brass Bridge triangle and Green Susans; barely reaching double figures. A very few may have made it into LBEs, but this sport is so difficult to check it is probably not even worth looking!
Imperforate sheets including these Open Door sports were prepared, in the same arrangement as the issued extra sports introduced in Spring 2005, and some sheets were perforated.

A close up shows how difficult it would have been for collectors to detect these sports, and so the idea, ingenious as it is, was shelved. Not because of concerns for collectors, because the problems experienced by the Weathervane sport had not surfaced then, but because even those packing stamps into LBEs would have needed a very good magnifier and a degree of experience to see these. Click on the pair to see a larger version, and still the sportiness is difficult to see. In the magnified image, the more open door is left, the slightly open door is in the middle, and the regular door is monochrome.

Extreme close-up photographs do not help much either. They do reveal differences between the two Open Door sports, and a common door, but it is just about at the limit of detection to the eye even with a magnifier.

 
Open Door 1                                            Open Door 2 Normal