In the newest edition of the ACSC (2015) relating to the KG V issues your orange 4d is under ACSC 110(2)
, referring to "Plate 2"
, and was printed circa 1919-1921. The plate flaw in the image shown is of the blue 4d (ACSC 112(2)eb)) it is in the final state (late state) of the plate deteriorating.
Your stamp seems to be in the early or intermediate state of the plate deteriorating, the late state of the orange 4d is catalogued at, and I quote "ACSC 110(2)eb) – later printing (deteriorates)"
unquote, and is priced at AU$1,000 MUH and AU$400 on cover, yours is unlisted, I wouldn't pass this stamp off as a common fault, far from it, as it is a plate flaw it may be a scarce or rare variety.
The early state is obviously much more valuable than the intermediate and late state of deterioration, but as the prices given is for MUH and on cover, I have no idea what the value would be for an unlisted used stamp, though I would expect it to rate more than a passing interest to a collector of plate flaws and the price to match it.
As it is used and not mentioned in the ACSC that one may or does exist it is impossible to tell if it is a one-of-a-kind which would give the stamp rare status, and very valuable.
Whether it be a one-of-a-kind or not, if damaged by tears (even repairs), thins, heavy hinge remnants, stains, heavy rust or foxing, this would have a very negative effect on the stamp even if unique.