Australia Scott 71, Acsc 102 Inverted Watermark

I have several used Scott 71 (ACSC 102) inverted watermarks. Per ACSC, most of these come from the 2/- booklets. The two used examples I have both clearly have the upper or lower perfs cut as to seem to come from booklets. However, I just picked up a mint copy that has nice clean perfs all around. ACSC goes on to say that watermark inverted from sheet stamps is scarce, but a number of sheets were issued and imprints exist. Is there any sure way to say that my mint copy is from a sheet or do we only have confirmation if it is an imprint or larger multiple? Just wondering.

Look at the horizontal perforations. Are the tips ragged on both sides or is one side showing straight perforation tips?

Straight perfs on the top of the stamp appear to be scissor / machine cut. So this is very likely from a booklet also.

The odds are very much against that being a sheet stamp. You would expect it to be torn from the sheet and, consequently, have very 'torn' perfforation tips.