Why Is Flat Press Plate Number Partially Missing?

I'm coming up to speed with the concepts of stamp collection, but was unable to find an answer for the following (but I assume its some problem during production)

I've seen several images of plate numbers printed on the flat press which are missing the lower portion or the upper portion of the numerals. (See example picture)



My questions are:

1) Is this a production problem or damage afterwards?

And if a production problem:

2) What causes it?

3) How often did it happen?

4) Is it viewed as more desirable, less desirable, or neither?

Bonus question:

5) What are the holes in the selvage? I've seen that on several plate blocks.

Thank you

1. production
2. mis-inked plates, they didn't quality control the edges as careful as the design
3. 7%, LOL not rare, not common
4. less desirable
5. the pads of sheets are stapled together for shipment to the PO's

Ding, ding, ding! We have a winner!