Two Plate Numbers On Coil Strips

Hello,

a plate number is the number of the plate that is used for the current printing, for sheet stamps as well as for coil stamps. For sheet stamps the concept of a plate is clear to me, but at coil stamps I don't get the complete picture of it.

Early coil stamps have - as I think - only one plate number per strip, but more recent stamps sometimes two numbers, like this one:

https://www.ebay.com/itm/US-1402-19...153097285105

It's called an EFO there, so I guess it's not the normal way. But when I look at the Durland catalog, many examples are shown with two plate numbers on one strip.

Also, I can't discover any rule about the sorting of the numbers, when I look in Durland. Sometimes it's (my examples):

35001 - 35002

sometimes

35002 - 35001 (opposite direction)

or even

35110 - 35100

So how did this work in the printing proces of coil stamps, that there are 2 numbers on 1 strip (=1 paper), and even in the wrong counting direction?

When did this start, so were there also more than 1 plate number on early coil strips?

two plates mounted on the cylinder, each one wrapping half way around, plate number at each end of the plate, so you get 01/02 at one place where the plates meet and 02/001 at the other place

just called EFO's because it requires a miscut for the plate numbers to show

thank you, good to know that, with the EFO and the two plates around the cylinder (actually thought it was 1 plate). I looked in Google a while but did not find how that looks like in the coil production.


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ok I had another look in the Durland.
The early rotary coil stamps only show one plate number, also later (1930s and Prexies) I only find strips with 1 plate number.

The first time I found 2 plate numbers is in the 1954 issue, being the exception, not the rule.

For the 1970 issue (as in my link above) only one example is shown, with 2 plate numbers. Also the 1975 issue shows 2 numbers.

So was the 1970 issue the switch from 1 plate to two plates around the cylinder, or was there just only 1 plate number at one end of the plate before?

But when were there some - not all - line pairs with 2 plate numbers in 1954 already?

To ask in another way: is there any rule when there were 2 plate numbers showing and in which sorting?