Great Britain Sc#43. PL 12 With Error :inverted Wmk#23.

This is Great Britain Sc#43. Pl 12 with ERROR :Inverted Wmk#23.
Could you please inform me about this Error. Is the Inverted Wmk 23 rare or common for this issue.? As well as What is your opinion about marging of left side of this stamp. Is it missed perforation or not.
Thanks for cooperation

Some plates have the inverted watermark as a rule. Plate 12 has both, no difference in price.
The 4d wmk "Garter" stamps were printed in panes with a wide margin between the stamps with letters F and G in the southeast corner. This was perforated through, resulting in wing-margined examples. The wing margin has been cut off.

Your stamp also has very short perforations on the other sides and is a spacefiller.

If there is any value at all, it would be from the underprint.

Dear NSK,
Thanks a Lot !!!

NSK is this a stamp dealers underprint or might ot be trying to do the same job as a perfin; ie antitheft?

These are unofficial protective underprints. Like the overprints, they were intended to prevent clerks selling them back to the Post Office.
There is an appendix in the old volume 1 'Specialised.' I do not see this one listed. But the appendix states SG hopes to include a full list of known underprints in the future. The part 2 of the revised volume 1, however, is almost four years overdue. I doubt it will be published soon.

Dear Noocassel. & NSK

Thanks a Lot!!!