Permissible to Copy Text Verbatim from Other Sources

Is it permissible to copy text verbatim from other sources into the Comment field of a Numista coin/banknote/exonumia page?  Is it enough to just add ©XYZ at the bottom?  Looking at the coin pages for this forum post https://en.numista.com/forum/topic142104.html many of the coin pages listed copied the Heritage Auction descriptions word for word.

Just now I was looking at this coin page N#197486 . The comments were taken directly from here:  https://coins.nd.edu/ColCoin/ColCoinIntros/NovaPatterns.intro.html with (source: Louis Jordan, coins.nd.edu) tacked on at the end.  

What are the rules for copying from other sites, books, etc?

Our guidelines https://en.numista.com/help/general-guidelines-for-all-texts-186.html state that 

“Never copy an original text that you did not write without citing its source.”

But we never limited the volume of citations within pages. I know also many coins just copying comments from commercial websites like here: 

N#327475

https://www.mint.ca/fr/magasiner/pieces/2014/fine-silver-coin---tradition-of-hunting-canada-goose---mintage-10000-2014

So just the addition of Source: XYZ is sufficient? No need to ask permission of the source?

The Copyright Statement from the coins.nd.edu site contains, “You should not assume anything in this site is in the public domain,” and “Permission to reproduce may be required.”

Citations with source are authorized by law. At least in France, only limitations are when:

- one creation is made of too much citations (like 50% of a book is citations from another book = parasitism)

- one creation is too much cited by another (like 50% of a book is copied in another one)

So everything is about proportion.

Numista is made of hundreds of thousands of pages, so first case is not likely. 

But indeed we shouldnt copy too much from the same source: even with source indicated, at some point we'd need authorization from author and publisher

Well explained.  Thank you.