Just Got This Back A While Ago.

Some research reveals that there was a range of dates for Australian Two Cents coins that have no 'SD'.

The opinion offered is that the 'SD' is due to the tiny letters in the die, which are subject to grease filling. In can be inferred that as a result, the coin pictured is a minor error, not a variety.
Nevertheless,
'no SD' Two Cents coins are relatively scarce, and as such, can be valued at $50 of more in uncirculated condition.

"SD" are the designer's initials. I have personally spoken with him may years ago on the subjects of jewelry and coin design. He thought that his most successful coin design was the Australian 20 Cents coin, which is still currently issued. He opined that showing the platypus under the surface of water in a round frame coin design was a difficult task, but ended up being very well interpreted.

He was once appointed as Goldsmith to Elizabeth 11. Now deceased.

P.S.
As this was a mint created issue without the initials of Stuart-Devlin (SD) and INTENTIONALLY used by the mint and not an error coin that makes it rare. Few people of the time collected them so the survival rate is only a few. Of those years mentioned above the 1966 No-SD is the rarest IMHO having tried collecting all associated dates (1966, 1967,1968 and 1981).

Yes, there are strikes from "grease-filled-dies"and "hub-doubling" but they are different.

Regards (JH from Beacroft)

It was in "Letters to the editor" along with the discovery about the 1981 20 cent with scalloped lettering-then graded and both authenticated by the ACGS (no longer active)

Do you remember which issue that year?