I've been trying to read a book on the Italian Imperial definitives, but it is in Italian so it's not easy! I do try and put phrases into "Google translate" but even then I sometimes have to guess what it is they're trying to say. I managed to get a few corner blocks from the set with information in the margin that let's you pinpoint which print runs they came from and when they were printed. The oldest one I have is the 2c depicting the Arms of Italy.
The oldest print runs had a number on the bottom left margin. I'm still not sure whether that is a proper cylinder number or more like an order number. I believe it is actually the latter because normal cylinder numbers would normally just start at 1 and each value (needing its own cylinder) would then have a cylinder 1. Which is not the case with this set, so this may well be cylinder no. 196 used by the printers. But no matter, for this number indicates that this printing was the original one, from 1930. A second print run, in 1938, had number 1178.
Later print runs, from approximately 1935 onwards, usually no longer had this number, as can be seen on this 15c Italia turrita.
This numberless block dates from 1939. One thing I am sure about is the dots in the corner. The cylinder could print four blocks of 100 stamps in one rotation. The printed paper was later cut into sheets of either 200 or 100. The four blocks of stamps were given dots from 1 to 4 so that the original position of the stamps on the cylinder could be retraced in case of flaws.
And then there's the Novara printings, after the war, such as this block of 35c Italia turrita stamps.
The Novara printings were emergency printings, in times when chaos still occasionally reigned in Italy. Officially, all stamps with the fasces symbols had been redesigned with the symbols removed, but for some of the Novara printings the old designs were still used. These can normally be disntinguished from their pre-war cousins because they have no watermark. The printing information on these is uaually on the right hand side, which is why this 35c black has to be a Novara printing, seeing that it has nothing printed in the bottom left corner. Also note the extra perforation hole in the left hand margin. I'm not sure yet whether this, too, is typical for the Novara printings.
As you see, so much still to find out!