The problem I have always had with the term "double print" in relation to modern stamps is that it means that the stamp was printed twice and I do not see how that is possible with modern reel fed presses.
And even if the printing is from single sheet fed processes, it is unlikely to occur when this is not done manually. Furthermore, a double print is as it says: printed double.
When one of these prints is in a completely different "shade" you are likely talking about transfer. Some consistency in the colour should be expected in a single printing.
Furthermore, you would expect full doubling of the image at similar quality, i.e., not with much reduced thickness / size of lines and letters.