Australia Sideways Watermark

This was a little pricey, but I needed a copy for my collection. Sideways watermarks are rare, but not really for this one. Identified as Scott 51b, ACSC 33aa, Mint Never Hinged.

Front Scan:


Through Scan showing full sideways watermark, plus a partial one:


I wonder about the vertical perforation spacing at the top of this stamp. It appears to be different than all of the others. Any comments from our Aussie friends?

My example is used & IF genuine is rare . But I'm not confident .

Thanks for the example Al. It looks like the same perforation pattern, so I guess that was the rule for these items. That cancel does look a bit dodgy, though.

These are new to me, I do not recall seeing them before.
I have seen examples of "comb perforator slippage"
generally in the last line of punctures before the table hit the stop pin.