Here is a Queensland adhesive duty stamp I'm trying to identify.

The stamp is from the 1920 or 1926 issue, as seen in this snip from the
http://ozrevenues.com website.

My stamp is perf. 12 1/2 and watermarked Crown over Q sideways, which doesn't help me to determine which issue it is from.
Can anybody provide additional information (or links) that will help me determine the proper issue? I want to create an album page for it (and it's siblings, if I ever obtain more from the series).
Thanks, and all responses will be greatly appreciated.
Robert