A couple of things I would point out.
Firstly, in 1922, they didn't have
good macro-photography flash technology available to them, and shiny coins (gold and silver especially) couldn't be photographed well without looking washed out or over-exposed. From what I've read, they got around this by making plaster casts of the coins, painting those a neutral flat color, and then photographing these casts, likely using daylight for the exposures. This is perhaps the process you are talking about.
If, instead, you mean the process of reproducing photographs in a book format, there is a great read on the evolution of that process here:
https://www.loc.gov/rr/print/coll/photographically-illustrated-books-and-photobooks.htmlI don't think any of that would explain the artifacts on the plates though.
You also have to remember, that in those days, they would photograph with a large frame film camera, not 35mm, and because film was expensive, a
good many coins would be on the same oversized negative. When those negatives were later used to create photographs suitable for printing operations, any issues with the celluloid negative
fabric would show as "scratches" on the exposed image, much like you see in your
catalogue.
If I were a betting
man, I'd say the negative got scratched before the
catalogue went to print, and for cost or schedule reasons, they used the images anyway, instead of re-shooting the coins. This could easily happen if, for example, someone pulled the negative in and out of an envelope carelessly, rested heavy objects on it in the office, dropped it on a dirty floor and then brushed it off, or whatever. They were fragile items.
Back in the day, these plates were used to sell coins - they likely weren't produced thinking someone would
still be referencing it 100 years later. If the images were
good enough to sell the coin, then they were
good enough to serve their purpose.