How Did Engravers At Babn In 1980 Make Changes To An Engraved Cylinder?

Hello PJR. The type of plate or cylinder you may be familiar with is completely different from this. Goebel manufactured a stamp printing press using five cylinders. Four of these are called gravure and each prints a different colour. They are printed consecutively. First is the grey queen's face and shadowing. Next cylinder is the green around the queen's face. Next is the tagging you call phosphor. There is now a spare space for another gravure colour not being used in this pane printing.
The fifth cylinder cylinder that follows on this sequence is the engraved cylinder that prints three colours at the same time. The cutting guides are the same colour as the 1 cent stamp, different from the 5 cent stamp and the black writing on the 17 cent stamps. Remember that this is printed on a huge roll of paper and rolled back into a roll at the end of the press.
This engraved cylinder was not completely remade but the cut guide design lines were changed. All 72 little 2mm x 5mm designs were "erased" and "re-engraved" not once but twice during the life of this cylinder. All the old flaws stayed. Flaws on this cylinder after the change stayed till the end.

I've been baffled by what I think is very complicated work. Even AI has not been able to explain how this small meticulous work is done. That is why I have turned to this forum in the slight hope of finding a person who may have done this very type of work with their own fingers. I know how secretive these processes were but this type of printing is now more mostly in the past. Even Goebel cannot help because there are no accessible archives available. Are there still a few living specialists alive?

bk80 Next is the tagging you call phosphor
The tagging is always applied last (unless it is contained in a light colour for shape tagging). In this example, there are two phosphor bands running over each stamp which "proves" the taggant was applied last.

The Goebel 500 has two stations:

First station. An engraved cylinder, capable of printing a maximum of three colours (the old Gualtiero Giori trick).

Second station. Four photogravure cylinders, each printing one color.

I don't know how many colours were printed by the first station and by the second station. But obviously there were enough photogravure cylinders to "abuse" the last active photogravure cylinder for tagging purposes.