There are various theories, all unconfirmed, as to the meanings of the numbers within this series of Maltese Cross cancellations. About the only thing people agree upon is that the number 12 canceller was likely used at a desk that dealt with larger items, as it is mostly known on multiples of the penny red or on the twopence blue. This is one reason that the 12 is the scarcest of the penny red numerals.
This series of cancelers was used in London from March/April, 1843 for about a year.
There are a few items known with strikes of two different numerals. Again, reason unknown.
There is a large section on these MX cancels in Volume 1 of the three-volume
Encyclopaedia of the Maltese Cross by Rockoff and Jackson. They also have more to say, including a census of multiples and unusual examples (e.g. on penny blacks) in Volume 3.
For the blues, if it's an 1841 blue (with the white lines at the top and bottom), it has to be plate 3. Plate 4 was not issued until after the end of the Maltese cross period when the plain numeral cancellations became standard. Copies of one of these on either a penny black or 1840 twopence blue (without the white lines) are rare and therefore valuable.
It is not too hard to assemble a set of 1-12 on penny reds. In fact, if you really wanted such a set, you probably could put it together on
ebay right now. However, the blues are much scarcer. As has been pointed out, prices for them are between 2 and 10x the price of those on the penny red. Consult a Gibbons Victorian Specialized catalog for current "catalog" value, though Gibbons catalog is not really representative of reality - figure about 1/4 to 1/2 of those values for anything but the most outstanding examples. For high-end retail prices, you can check Arthur Ryan's site and look at his stock list prices (
http://www.gbstamps.co.uk/queen_vic...vanced.asp). Depending upon how deep this link takes you, you might have to select "Stamp Price List;" then "Queen Victoria;" and then scroll down til you see the listings for SG catalog number 14f).
I've managed to put together a set of the numbers on the penny reds and I have 4 of them on twopence blues. I made it a bit more difficult (what else is new?) by restricting my collecting of QV imperforate line engraved to only copies with my initials as the corner letters (1 out of 240 on the sheet). Examples below.
The blues are a nice find. Congratulations.
Chip

