Hi Wert,
I do not have many of this stamp, but of the 18 I have there are none with this variety. I am guessing that it is a variety because it is a 'white' dot. Which means that something was removed from the plate to stop the ink from making its mark. If it had been an addition, like a fleck of paper or other small piece of trash then it would have left a 'black' ink mark.
Here is an excerpt from the publication "Constant Plate Varieties of the Canada Small Queens" by Hans Reiche, that gives some information about the 1/2 cent small queen.

Well done!
- stamporator --