Australia EFO - Or Not?

While looking through some Australian material, I ran across a stamp which had what I thought a fairly common flaw in the lower right denomination tablet. It was a void in the inking that is usually associated with a bit of debris either on the paper or on the printing plate and I identified it as such. Later, in the same batch of material, I found a second stamp with almost exactly the same flaw which immediately sparked my interest.

They are both on copies of Scott #21 with the Wide Crown, Narrow A watermark and, though very similar in placement and in shape, there are differences between the two flaws. A couple of questions here. Firstly, am I missing a constant variety here or are they indeed in the EFO category? Secondly, what might be the explanation for two very similar errors both in placement, size and shape? Could they conceivably be the same bit of debris being retained on the plate? Though to create the void in the ink, I would have thought that the speck would have disappeared on the first pass.

I don't think this flaw was associated with a foreign object on the plate. After all, the flaw exists on the initial proofs and was present all the way to 1928. At that point, the cliche was reentered to eliminate it, in the process creating seven or so new flaws!

That is interesting. So it is a constant variety through at least a part of the life of the stamp.

Is there a link that you could recommend to read up on this? In any case, thank you for the information.

I am not aware of anything along those lines specific to this stamp. For the 1d sideface, I generally check with the BSAP checklist. For each variety it gives the various states each stamp goes through for the life of the stamp, including proofs. The beauty of listing multiple flaws, unlike ACSC which generally lists only the major flaw, is that secondary flaws can act as verification for the selection of a plate/pane and position. Unfortunately, your stamp doesn't have any secondaries in its initial state.

Another advantage of checklists is that they generally flag cases where another position has a similar flaw and the presence or absence of a secondary flaw becomes necessary to determine its correct position.