1940ish French Corner Blocks. Date Of Printing?

I bought a set of corner blocks a long time ago, and finally had time to look at them. Not very costly, or valuable. My question concerns the number in the corner. I'm almost certain that this is a control number which is the date of printing. I would expect this date to be just before to many months after the date of issue. Using Stanley Gibbons as my guide, here are two which seem correct. (SG 684, 685) The 2F25 blue was issued 30.1.39 (January 30, 1939), and the control number is 14.6.39 (June 6, 1939). The 2F50 green was issued 20.1.39, with control number 13.10.39. These were both surcharged with 1F in red in 1941, so I guess the stock was just around for quite awhile.





My real question concerns this one. SG 722 issued 27.12.41. Can someone help me figure out the control number?

My guess is that for the two Ceres head blocks, since the numbers are separated into groups with dots,they therefore, are as you surmise dates: June 14th, 1939 for the blue one and October 13th, 1939 for the green one, and my guess is that these are the printing dates. Note that both are from the lower RIGHT corner of the sheet, but the third one with Marshall Petain is from the lower LEFT corner, and the numbers are not separated into groups by dots, and they don't in any case, form anything like a believable date, so I suspect that these are control or plate numbers. So, that's my guess: date of printing on the lower right corner, plate or control number on the lower left.
And here's something interesting I noticed about the design itself of the Ceres head stamps. The only indication of the country of origin, is the intertwined letters RF - for Republique Francaise in the upper left corner, and in the upper right corner, more, I suppose as a design element, and for the sake of symmetry, is the same device, only in mirror image. I don't know of another example where this has been done on a stamp: the name, or at least the initials of a country, only reading backwards!

Switzerland also printed the date on stamp sheets until a lot more recently. Perhaps they still do.

Great info. Thanks everyone.

Here is one from the French occupation of the Saarland.