The 2c carmine from the Numeral issue was not ready for issue until August 22, 1899, so in the interim period from July 31, 1899 until then, there was a shortage of 2c stamps. Something had to be done.
The Post Office Department decided that rather than waste the existing stock of 3c Numeral stamps, they would be overprinted with a simple surcharge to reduce their value from 3 cents to two cents:
Deep bright carmine Pale rose carmine
Carmine Deep bright rose carmine
The shade differences are subtle, but I suspect that if you collect them in large multiples, they will be much more obvious. The shades that I have seen so far on the stamps are as follows:
1. Carmine (very common)
2. Pale carmine
3. Rose carmine
4. Bright rose-carmine
7. Deep bright carmine (very common)
1. Deep carmine-red
2. Deep rose-scarlet
3. Deep bright carmine-red
5. Dull carmine-red
6. Bright carmine red (most common)
Unitrade makes no distinction between these, calling all the stamps simply "carmine". I'm sure that the above list is by no means exhaustive and that there are other shades besides what I have listed there. Some of them are clearly more common than others, as I have indicated in parentheses. A study aimed at establishing the relative scarcity of the shades could be a very rewarding study project.
The normal spacing between the surcharges on adjacent stamps is 7mm as shown between the first and second columns of the above block. However, a narrow spacing variety exists in which the spacing is 4mm. It just so happens that this variety is present in the above block between columns 3 and 4. Normally the variety is collected as a strip of three, so that the difference can be readily seen. However, it can also be collected in pairs, given that the dimensions of both types are now well known.
In addition, some stamps are known with inverted surcharge, and with the surcharge on the back of the stamp:
There is some disagreement among specialists as to the authenticity of these errors. I'm not exactly sure why, since the characteristics of the overprint on these stamps exactly matches the other issued stamps. I'm guessing that it is because there is no official record of their discovery. However, regardless of whether or not they are genuine, they are nonetheless interesting in my opinion.
Studying the Effect of Wear on the Surcharge
To my knowledge, I have never seen anything written on the surcharge itself, although I have noticed very clear varieties in both the thickness and clarity of the letters. I have also noticed that nearly all of the Numeral stamps have very thin, clear letters, while most of the Maple Leaf stamps have thicker letters that are sometimes very thick, and nearly all show signs of wear:
Multiples and Plate Blocks
I have seen very few used multiples, so I must conclude that they are quite scarce and definitely worth pursuing. Mint multiples are not to difficult to come by, but plate blocks are scarce, and form a very interesting topic. Why? Well this issue was made from remainders of the regular 3c stamps, which were printed from many plates. So it is unlikely that stamps exist from every single plate that was used to print the 3c stamps. However, there is no guide book that I know of that definitively lists all the plate blocks of this issue that exist. Below is a plate block of 8 from plate 6 of the Maple Leaf stamp that sold for $180 in a recent Spink auction: