Where did "boilerplate" and "-30-" come from?

Two questions were asked today – Why "-30-" at the end of a media release and where did the term "boilerplate" come from.

Still doing some digging but this is what I know so far –

Boilerplate (from Wikipedia):- The term dates back to the early 1900s, referring to the thick, tough steel sheets used to build steam boilers. From the 1890s onwards, printing plates of text for widespread reproduction such as advertisements or syndicated columns were cast or stamped in steel (instead of the much softer and less durable lead alloys used otherwise) ready for the printing press and distributed to newspapers around the United States. They came to be known as ‘boilerplates’. Until the 1950s, thousands of newspapers received and used this kind of boilerplate from the nation’s largest supplier, the Western Newspaper Union.

-30- (from Press Release Writing): The "-30-" is the traditional journalistic closing which probably came to be during the Civil War when telegraphers tapped "XXX" at the end of a transmission, which is the Roman numeral for 30.The "-30-" is the traditional journalistic closing which probably came to be during the Civil War when telegraphers tapped "XXX" at the end of a transmission, which is the Roman numeral for 30.

If anyone has additional or differing information, please let me know.

Ciao!