Hong Kong 1876 perf question

A friend has raised a question that other readers of rcsd probably can
answer. Any and all help would be appreciated. The stamp in question
is shown at:

http://cjoint.com/?ADrbo9QgQ5t

Here's another stamp I can't find in Scott. It's Hong Kong Scott Type
A1, the 18 cent with 16 cents overprint, and would seem to be Scott
29. However, it's perf 12 1/2 and Scott 29 is perf 14. In fact, all
Scott Type A1's are perf 14. Could it be a variety noted in Gibbons or
some other catalog?

I couldn't find any info on the APS site or on the web.

Thanks for your help.


Stan