My apologies for never replying to your answer - most helpful, thank you! And thanks so much for the 1869 EKU scan, which I had not seen before.
I think I ought to get around to obtaining a certificate someday.

Passage East.JPG The SG Specialized gives a put-to-press date for the 1 Shilling green, plate 6, of March 20, 1872, but notes that the plate was registered three years earlier and that genuine covers exist dated March and April, 1869 - presumably franked with examples from the "five extra shee...

As you can see from these two examples, dates could be faulty. The one on the left is a Dublin cancel missing the year date altogether (most likely 1872, but who knows?) and the one on the right has had the date (24) inserted in pen-and-ink, presumably by a conscientious postal clerk. 1s cds date er...

Keep in mind that the dates in cancels are not 100% reliable. For example, in the one you've got, there could be a digit missing (1, 2 or 3) in front of the 1, meaning it was actually cancelled on Oct. 11 or 21 or 31, rather than Oct. 1. This could happen if the little metal number was set wrong in ...