This is a comparison of images, not just catalogs of sources in images. If you look at the image in the linked article, you can easily spot one of the stars that has "gone missing".

Looking at the brightness of the source that went missing, it is hard to suggest instrumental error - much fainter stars remain detectable in both epochs.

And fraud, really? Who would bother to fake stars in catalogs and plates in the 1950s, and why?

>it is hard to suggest instrumental error - much fainter stars remain detectable in both epochs.

I think if there is an instrumental error it would more plausibly be the opposite. That the bright stars are artifacts in the images.

So they could identify who plagiarized their catalogs?

https://en.wikipedia.org/wiki/Fictitious_entry

Well you could, but why would you want to? Other than video games which didn’t exist in 1950, I can’t think of any reason someone would use a star catalogue in a for-profit scenario.

Should be a relatively simple matter to cross-reference against other photographs (potentially from other observatories) to identify whether the same star appears multiple times.

Or included as copyright traps https://en.wikipedia.org/wiki/Trap_street

Cartographers used to fight plagiarism with fictitious entries. Is it possible stellar cartographers did the same?

Cartographers get paid to make and sell unique branded maps, and they differentiate themselves by quality to make significant sales.

Stellar cartographers aren't selling unique branded star catalogs, so there is no reason to complain if someone has copied your data. The incentives are completely different.