The well known Die II Plate Flaw N20d Frame Break under N of PENCE Row 20.2 is worth a mention here. The more common control is T22 from the Plate 3 Printing. Two different controls or positions are noted with the 1922 printing under control T22 and are shown here. The 1923 printing under control W23 is not so easy. I have only seen one block of six showing this variety.

Plate 3 has the rule 20th left side tapering towards base as can be seen on the W23 Block of Six. The rule under row 20.2 is also generally thinner on the 1923 printings.

A close up view of the Plate 3 Frame Break Flaw.

My copy shows a distinct white flaw running from the left leg of 'N' in PENCE directly South, through the value tablets Orange background colour, onwards where it settles out as a grove on the inside edge of the outer most frame line
Any info would be appreciated as this flaw is somewhat 2mm or so to the left of that mentioned above.

Another image

The stamp above has been tampered with so please ignore the post, the Orange ink is certainly missing from the leg of N and below but some pesky fool has tried to improve it and failed. Tiny fibres are prickling and pointing about.
I have however found the correct N20d on another stamp hiding away in my block cypher file.
This one certainly shows the flaw in all its beauty in a Bright Orange shade.
Lee